Injured South Sydney centre Greg Inglis will be given until grand final day to prove his fitness for Australia's Four Nations rugby league campaign but Penrith's Michael Jennings is already eyeing his spot.

Inglis, who has not played since injuring his ankle in the Bunnies' round 25 loss to Brisbane at Suncorp Stadium, will be given every chance to prove he has recovered from ankle and knee problems.

But the dynamic ball-runner remains on crutches and it is understood his recovery may fall just one week short of the cut-off for the naming of the squad on October 3, the day after the grand final.

Inglis has just a fortnight to recover, and that potentially opens up one of the centre spots for a host of young stars - including Jennings and Bulldogs centre Josh Morris, with both to take the field for the Prime Minister's XIII against Papua New Guinea next weekend.

Jennings admitted he would be using the match as a way to force his way into the final squad for the end of season Four Nations tournament being held in England.

"It's an opportunity, I get that opportunity to really push for that position," he told reporters on Thursday.

"Playing in the Prime Minister's team is going to give me that opportunity.

"If i get picked I'd be grateful and honoured, and I'd love to represent that Australian jersey and take that position."

Jennings' Penrith team-mate Luke Lewis, who is a strong tip to make the Kangaroos squad, said the light-footed speedster would step up if called upon by Australia coach Tim Sheens.

"Jenko wouldn't look out of place," Lewis said.

"His attitude is spot-on at the moment. He knows what he wants in football, what he wants from rugby league.

"Greg Inglis is a big shoes to fill, he's a champion player. He's performed for Queensland and Australia every time he's played for them.

"It's definitely big shoes to fill but there's no better bloke to be able to do it than Michael Jennings."

Sheens confirmed a number of players who were unavailable to train at Thursday's session, including Inglis and North Queensland co-captains Johnathan Thurston and Matt Scott, would be given until the last minute to prove their fitness.

"Greg Inglis has had surgery on the knee, his foot comes out of the boot in the next couple of days ... It will be the knee issue, we'll give him until the last minute as well at this stage," Sheens explained.

"... With Johnathan Thurston just finishing on the weekend, we didn't ask him to run (on Thursday).

"(Scott) has (a back issue), again that will be assessed over the next two or three weeks,.

"He's not looking at surgery, at this point we'll give him at least until selection which is the game after the grand final."

Newcastle signing Kade Snowden was ruled out on Thursday after struggling with back and neck problems throughout 2010.

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