Sydney youngster Sam Reid and veteran Lewis Roberts-Thomson will return from injury in Saturday night's AFL elimination final against St Kilda but key defender Heath Grundy will miss the game after being diagnosed with glandular fever.

Reid was named in Sydney's team after proving he had overcome calf stiffness at Thursday's training session but Grundy, who like Reid was a late withdrawal from the Swans' last-start win over Brisbane, was unable to do the same.

"Heath was out on the training track today but he still felt lethargic and flat," coach John Longmire said.

"We just got the results back and they've now confirmed that he has glandular fever, it's very disappointing for Heath and for the team.

"He's been in good form all year and plays a key role in our defence. However his health is our main concern and we'll make sure he now gets all the rest he needs."

Grundy could still play in the finals series if the Swans beat the Saints with club doctor Nathan Gibbs planning to monitor him week by week.

Defender Roberts-Thomson will play his first AFL game since the side's shock 43-point loss to Richmond in round 21.

"He's played down back in grand finals before (2005), he's played forward for us this year and in the ruck for us this year. He's played well in all of those roles."

Nick Malceski and Lewis Jetta are the two players dropped from the team that beat the Lions by 52 points.

Adam Goodes and Jude Bolton will both be playing their 19th final on the weekend, setting a new club record, while six youngsters will be embarking on their maiden finals campaign.

And while Longmire expects the pair of veterans to help guide Craig Bird, Alex Johnson, Luke Parker, Sam Reid, Gary Rohan and Matt Spangher, he's sure the sextet's exuberance will prove just as advantageous.

"You've got the top end with some experience there and then some real excitement and youth coming in under it," he said.

"It's a nice blend ... I think the enthusiasm certainly rubs off on those older boys.

"They (Goodes and Bolton) probably will (say something) down in the locker rooms, pretty informally they'll have a chat to them.

"But I think they get a lift out of those young kids ... those kids are just really excited to be playing senior footy."

Bolton suggested it would be "on for young and old" against the Saints and that the club's quality youth stocks had provided a spark in September.

"With regeneration and a turnover of players, you definitely feel that energy that comes from those guys wanting to perform on the big stage," Bolton said.

"I think we'll definitely try to give them a little bit of confidence and basically say that it's another game.

"If you try and build it up too much in your head, play it out too much in your head, you probably overthink it a little bit."

"All the little things count, hopefully that's what we can impress upon our young guys."

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