New Zealand back-row forward Luke Jacobson has been ruled out of the Rugby World Cup in Japan due to concussion.
The All Blacks said that 22-year-old Jacobson, who won caps against Argentina and Tonga this year, was suffering "a delayed onset of concussion".
Jacobson had travelled to Japan as part of the New Zealand World Cup squad, but he will now be replaced by the Highlanders' Shannon Frizell.
All Blacks coach Steve Hansen said Jacobson had not presented with any signs of concussion after last week's game against Tonga, but developed symptoms following a first training session this week.
"After discussing this latest episode with Luke, as well as our medical team, the decision has been made to, sadly, withdraw him from the tournament," Hansen told http://www.allblacks.com.
14 Jun 1987: The New Zealand team do their Haka dance at the beginning of the Rugby World Cup match between New Zealand and Wales in the semi final in Brisbane, Australia. New Zealand won the match 49-6. (Russell Cheyne/Allsport)
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John Drake, Sean Fitzpatrick and Steve McDowell of New Zealand prepare to pack down for a scrum during the 1987 Rugby World Cup Semi-Final match between New Zealand and Wales at Ballymore Stadium on June 14, 1987 in Brisbane, Australia. (Ross Land/Getty Images)
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Serge Blanco of France makes a break during the 1987 Rugby World Cup Semi-Final match between Australia and France at Concord Oval on June 13, 1987 in Sydney, Australia. (Ross Land/Getty Images)
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David Kirk of New Zealand kisses the Willam Webb Ellis Trophy after the 1987 Rugby World Cup Final match between New Zealand and France at Eden Park on June 20, 1987 in Auckland, New Zealand. (Ross Land/Getty Images)
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Michael Lynagh of the Wallabies scores the match winning try during the Rugby World Cup semi-final match between Australia and Ireland at Lansdowne Road October 20, 1991 in Dublin, Ireland. Australia won the match 19-18 and went to beat England in the final. (Shaun Botterill/Getty Images)
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England captain Will Carling introduces Queen Elizabeth to the England team before the Rugby World Cup Final against Australia at Twickenham, 2nd November 1991. Australia won the match 12-6. (Russell Cheyne/Getty Images)
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Australian scrum-half Nick Farr-Jones (left) and winger David Campese lift the Webb Ellis Cup after Australia's 12-6 victory over England in the Rugby World Cup Final at Twickenham, 2nd November 1991. (Russell Cheyne/Getty Images)
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S. Poivedin, Phil Kearns and Michael Lynagh of the Australia Rugby Union team hold the Webb Ellis Trophy in the baths after the 1991 Rugby World Cup final victory over England (Allsport UK/Allsport)
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Sean Fitzpatrick of New Zealand is treated for a nosebleed during a Rugby World Cup pool stage match against Ireland at Ellis Park, Johannesburg, South Africa, 27th May 1995. New Zealand won 43-19 and went on to the final, where they were defeated by South Africa. (Shaun Botterill/Getty Images)
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Jonah Lomu of New Zealand evades the diving tackle of Rob Andrew of England during the Rugby World Cup Semi Final at the Newlands Stadium in Cape Town, South Africa. New Zealand won the match 45-29. (Simon Bruty /Allsport)
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South Africa's president Nelson Mandela congratulates South Africa's rugby team captain François Pienaar before handing him the Webb Ellis Cup after the 1995 Rugby World Cup final match South Africa vs New Zealand at Ellis Park Stadium in Johannesburg on June 24, 1995. (AFP PHOTO/JEAN-PIERRE MULLER)
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English players (From L to R) Darren Garforth, Martin Johnson, Joe Worsley and Dan Luger watch Samoan players perform the Haka before the Rugby World Cup quarter-final play-off game between England and Fiji 20 October 1999 at Twickenham stadium, southwest London. England won 45 to 24 and qualified for the quarter-final against South Africa. (OLIVIER MORIN/AFP/Getty Images)
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Semo Sititi of Samoa celebrates victory over Wales in the Rugby World Cup Pool D match at the Millennium Stadium in Cardiff, Wales. Samoa won 38-31. (David Rogers /Allsport)
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Jonah Lomu of New Zealand in action during the Semi Final match of the Rugby World Cup against France played at Twickenham in London, England. France won the game 43-31. (Ross Kinnaird /Allsport)
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The French team celebrate after beating New Zealand to win the Semi Final match of the Rugby World Cup played at Twickenham in London, England. France won the game 43-31. (Ross Kinnaird /Allsport)
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Australian scrum-half George Gregan (L) jumps to celebrate his victory as French fly-half Christophe Lamaison walks away after the Rugby World Cup 1999 final game opposing France to Australia 06 November 1999 at the Millennium Stadium in Cardiff. Australian won the final 35 to 12. (WILLIAM WEST/AFP/Getty Images)
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Australian winger Joe Roff drinks from the cup inside the locker room after the Rugby World Cup 1999 final game between France and Australia 06 November 1999 at the Millennium Stadium in Cardiff. Australian won the final 35 to 12 (WILLIAM WEST/AFP/Getty Images)
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Dave Rogers (Getty): This is Jonny Wilkinson kicking the last-minute drop goal to win the 2003 Rugby World Cup in Sydney. It was an amazing occasion for an Englishman to cover, the excitement was incredible. Fortunately, Jonny, who is predominantly a left-footed kicker, kicked this drop goal with his right and therefore was facing towards me.
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ngland captain Martin Johnson celebrates Englands victory with Neil Back and Ben Cohen during the Rugby World Cup Final match between Australia and England at Telstra Stadium November 22, 2003 in Sydney, Australia. (Photo by Cameron Spencer/Getty Images)
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Dave Rogers (Getty): This is the same occasion but it shows Clive Woodward, the England head coach, taking the Rugby World Cup back down the tunnel to the England dressing room. I have known Clive, since 1980 and it was an absolute thrill to see his dreams, and England's, come true.
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Hugh McMeniman of Australia contests a lineout ball with Mike James of Canada during the IRB Rugby World Cup Pool B match between Australia and Canada at Stade Chaban-Delmas September 29, 2007 in Bordeaux, France. (Photo by Cameron Spencer/Getty Images)
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Dave Rogers (Getty): This shows Andrew Sheridan, the England prop forward head to head with his opposite prop, Matt Dunning of Australia. Sheridan, probably the strongest prop in the world at the time, loved the challenge of taking Dunning on and I think this image shows how much he intimidated the opposition.
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The France team, wearing shirts representing the national flag, face up to the New Zealand team as they perform The Haka before during the Quarter Final of the Rugby World Cup 2007 match between New Zealand and France at the Millennium Stadium on October 6, 2007 in Cardiff, United Kingdom. (Photo by Stu Forster/Getty Images)
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Louis Deacon of England out jumps Cristian Constantin Petre of Romania during the IRB 2011 Rugby World Cup Pool B match between England and Romania at Otago Stadium on September 24, 2011 in Dunedin, New Zealand. (Photo by Shaun Botterill/Getty Images)
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Hannah Peters (Getty): A nice try picture is often hard to get in rugby union as you're often quite far away from the action and you need a few things to go your way. A good dive always helps and also clean backgrounds behind the players and crowd.
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Mike Phillips, Alun Wyn Jones and George North sing their national anthem ahead of the quarter final one of the 2011 IRB Rugby World Cup between Ireland v Wales at Wellington Regional Stadium on October 8, 2011 in Wellington, New Zealand. (Photo by Stu Forster/Getty Images)
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Sam Warburton of Wales upends wing Vincent Clerc of France during semi final one of the 2011 IRB Rugby World Cup between Wales and France at Eden Park on October 15, 2011 in Auckland, New Zealand. (Photo by Stu Forster/Getty Images)
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Hannah Peters (Getty): This image was shot from the roof of Eden Park in amongst the light towers when the All Blacks beat France to win the final in 2011. I was harnessed in and attached to a minder so making the right lens choice and praying the play went my way on the final whistle were all big factors in making this image work.
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Captain Richie McCaw of the All Blacks celebrates winning the 2011 IRB Rugby World Cup Final match between France and New Zealand at Eden Park on October 23, 2011 in Auckland, New Zealand. (Photo by Cameron Spencer/Getty Images)
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The All Blacks had a few parades around New Zealand after winning the Rugby World Cup in 2011. I was waiting for a few hours on top of a ladder for Richie McCaw and the World Cup to arrive. Luckily, he held it up just as they drove past a New Zealand flag to place the picture.
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Dan Mullan (Getty): Finally, here is Israel Folau of Australia competing in the air against Metuisela Talebula and Asaeli Tikoirotuma of Fiji during their match in Cardiff. Folau was known for his aerial prowess and this image displays it perfectly, winning the ball against two of his opposition.
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A general view of the action during the 2015 Rugby World Cup Pool D match between Ireland and Romania at Wembley Stadium on September 27, 2015 in London, United Kingdom. (Photo by Shaun Botterill/Getty Images)
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Francois Louw of South Africa leaps on to the back of Sonny Bill Williams of the New Zealand All Blacks during the 2015 Rugby World Cup Semi Final match between South Africa and New Zealand at Twickenham Stadium on October 24, 2015 in London, United Kingdom. (Photo by Shaun Botterill/Getty Images)
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Dan Mullan (Getty): In this image I captured Adam Ashley-Cooper of Australia diving over to score one of his three tries in the semi-final against Argentina to send his team through to the final. I liked this image as Adam is in full flight diving for the try line with the capacity Twickenham crowd watching on.
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Dan Mullan (Getty): Another one from the semi-final between Australia and Argentina, here’s Scott Fardy spitting after being cut on the head. This image really stood out for me as something a bit different, it was away from the action and an isolated portrait that showed the brutality of rugby.
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Richie McCaw of the New Zealand All Blacks lifts the Webb Ellis Cup following the victory against Australia in the2015 Rugby World Cup Final match between New Zealand and Australia at Twickenham Stadium on October 31, 2015 in London, United Kingdom. (Photo by Shaun Botterill/Getty Images)
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"We all felt that the best thing for him to do is to take a break from rugby until he is symptom-free and ready to return to rugby." PA.
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