Cassidy has completed a six-match ban for a high tackle on Leeds' Adrian Morley - one of the players he could face at Old Trafford next Saturday - and Monie has brought him straight back into an otherwise unchanged team.
The Great Britain utility forward will start on the substitutes' bench, replacing Jon Clarke. Danny Moore and Terry O'Connor retain their starting places, ahead of Paul Johnson and Neil Cowie, as Monie defuses any uncertainty at a uniquely early stage.
Their in-form stand-off, Tommy Martyn, believes that he is another St Helens player to be overlooked for Great Britain's Test series against New Zealand.
Martyn, one of Saints' key men this Sunday when they contest the remaining Grand Final place with Leeds, says that he, like his team-mate, Anthony Sullivan, has not heard from the national coach, Andy Goodway, and does not expect to be included.
The Leeds coach, Graham Murray, has urged Goodway not to disregard another of the leading candidates for the stand-off role against the Kiwis, his captain, Iestyn Harris. Unofficial indications are that Harris might not be in Goodway's starting line-up.
"He's got to be in the team," said Murray. "He's one of the best players in the country."
Harris, along with his team-mate Morley, who is struggling to recover from a shoulder injury in time to face Saints, is among the nominees for the Super League Players' Player of the Year award, to be announced next week. The other player shortlisted is Wigan's Henry Paul.
Morley, along with Terry Newton and Marc Glanville, is described as making "steady progress" as Leeds strive to get him fit for Sunday.
Barrie McDermott, Dean Lawford, Graham Holroyd, Marvin Golden and Tony Kemp have all been added to the squad as cover for the doubtful trio.
The Kiwi coach, Frank Endacott, took time out from preparing for today's deciding Test against Australia to promise that, despite the loss of players like Richie Blackmore and Matthew Ridge, he will be bringing a formidable squad to England.
"I think people in Britain will be surprised by the quality of our team," he said. "They are going to find out quickly that we have another batch of world stars coming through."
Jason Flowers has signed a new contract at Castleford, who have released four players - Andrew Schick, David Chapman, Mike Mord and Richard Russell - and lost Jason Critchley to Newport rugby union.Reuse content