ST KILDA midfielder Luke Dunstan will have surgery on his dislocated left shoulder but the club expects him to be fit for the start of pre-season.

He will likely be operated on early next week, after the swelling in his joint has subsided. He suffered the injury in last Sunday's win over Carlton when trying to tackle Ed Curnow.

It will take 16 weeks for the 21-year-old to recover, but he will be able to run during that time.

Coach Alan Richardson said at Moorabbin on Friday his side faced a tough challenge to combat the Sydney Swans' midfield on Saturday night at Etihad Stadium, in a must-win game for the Saints' faint finals hopes.

"Blake (Acres) and 'Gresh' (Jade Gresham) will have to play a little bit more time through the middle of the ground," Richardson said.

Dunstan, 21, ranks fourth at the club for contested possessions per game, and his loss will be significant considering the Swans are the No.2 team for contested ball differential.

After being dropped three times this season, Acres has hit solid form. He was the round six nominee for the NAB Rising Star Award but his last couple of weeks have arguably seen him in better form, averaging 10.5 contested possessions in that time. 

"He's been much better in terms of consistently winning the ball in contest. He's looked more competent with the ball in his hands. His efficiency by foot is heading the way we'd like it to," Richardson said.

Paddy McCartin was named to face the Swans for his first match since round 15 against Gold Coast when he was concussed for the third time this season.

The 20-year-old played in the VFL for the past two weeks and kicked five goals against North Ballarat in his most recent performance.

The forward trained away from the main group in a light session, along with Jack Billings, Josh Bruce, Tom Hickey and Dylan Roberton. 

The Swans clash will be Roberton's 100th game. 

All three emergencies – Daniel McKenzie, Cameron Shenton and Jason Holmes – trained.

Although the Saints have multiple big men in attack, Richardson was not worried about the prospect of being too tall and adversely impacting his team's defensive pressure. 

"We've had those guys in the same team, not always in the front half. We think those guys can be a real threat," he said.

Nick Riewoldt has spent more time up forward in the absence of McCartin, and Richardson envisages the skipper will spend his time in the forward 50 and on a wing.

"The Swans are going to be a real challenge (in terms of) getting the ball from one end of the ground to the other. They're very good defensively and 'Rooey' can give strong connect," Richardson said.

"We'll need him to be in front of the ball and we'll need him in the midfield."