Billy Vunipola injury: England No 8 ruled out of Rugby World Cup 2015 with Nick Easter called up as a replacement

Easter was seen at England's Bagshot training base today and has replaced Vunipola in the 31-man squad

Billy Vunipola has been ruled out of the rest of the World Cup (Getty Images)

Billy Vunipola has ruled out of the rest of the Rugby World Cup after suffering strained knee ligaments in the defeat to Wales, with Harlequins No 8 Nick Easter called up in his place after he was seen at England’s training base in Bagshot.

The Saracens back-row was instrumental in putting England ahead against Wales on Saturday, but his departure with a knee injury coincided with a shift in momentum as Wales fought back to claim the thrilling Pool A encounter 28-25.

Vunipola is just the first of a number of injury concerns for England as head coach Stuart Lancaster weighs up the cost of the demoralising defeat. With Vunipola now playing no further part in the World Cup, Lancaster must assess the fitness of Courtney Lawes and Ben Youngs as the pair also left the pitch injured, while Ben Morgan and Jonathan Joseph continue to struggle with existing injuries.

England head in to their must win encounter with Australia this weekend having lost one of the most prominent figures in recent games. Vunipola excelled in the absence of Morgan – who miss the bulk of last season with a broken leg – and was one of the best players in this year’s Six Nations championship.

Billy Vunipola has been ruled out of the rest of the World Cup (Getty Images)

Vunipola will miss up to six weeks, meaning that he would not have recovered in time to feature in the World Cup final on 31 October if England somehow upset the odds and reach the showcase game at Twickenham.

"It's so unfortunate for Billy but the scan shows an injury which means he can't take any further part in the World Cup," head coach Stuart Lancaster said.

Vunipola took to Twitter to confirm the news himself, and he admitted that he is “gutted” to see his World Cup end after just two matches – the first of which he started on the bench behind Morgan.

Lancaster added: "Billy worked really hard and committed everything to the last three months," Lancaster said.

"He is a young man with a bright future ahead of him and I know he will be an integral part of this team for years to come.

"Nick was unlucky to miss out on final selection. He is a specialist number eight and an experienced player. We know he will make a big contribution."

The call-up for Easter, who will now feature in his third World Cup after being part of the 2007 and 2011 squads, proved to be a straight-forward one, with the 37-year-old veteran the unlucky man to be axed from the final training squad when Lancaster whittled it down to 31.

James Haskell is likely to be given the No 8 role if Morgan does not recover in time to face the Wallabies, although there is a case to be argued that Easter could start having come in as the fresher option. However, Haskell only played 17 minutes against Wales and did not feature in the win over Fiji, while Easter has been going through pre-season training with Quins.