LUCKLESS St Kilda forward Paddy McCartin is expected to miss about three games as he deals with a low-grade left foot sprain, but he could be sidelined for longer.

Meanwhile, star defender Jake Carlisle trained on Monday after suffering a punctured lung but is no certainty to face Carlton on Friday night.

McCartin was hurt four minutes into last Saturday's loss to Port Adelaide but played out the match, collecting six disposals and booting two behinds.

It is a similar injury to the one he suffered during the pre-season, albeit less severe and to his other foot.

Coach Alan Richardson told AFL 360 McCartin would spend a fortnight in a moon boot.

"A bit lucky, if you can call missing a couple of weeks lucky, so Lisfranc, if it had have been, then that's a long time (out)," he said.

"He'll be completely laid up for a couple of weeks with the boot, so he's going to take a little while after to get going."

Richardson thinks the 22-year-old could return in 2018.

"We're really hopeful that he'll get back before the year's out," Richardson said.

St Kilda football manager Simon Lethlean told saints.com.au McCartin should be out for no more than three matches.

"Paddy played out the game with some discomfort and while not overly serious, it will require him to spend time in a moon boot this week," Lethlean said. 

"We'll reassess how it is at the end of the week and have a clearer picture on how quickly he can get back into training. 

"It's obviously a frustrating setback, but thankfully a fairly minor one that should only keep him out for two-to-three weeks."

McCartin has played 13 games this year, the most he has managed since he was drafted with the first overall selection in 2014.

Carlisle may not return this for Friday's clash.

"He's a chance. He's not a certainty but he's heading the right way," Richardson said.

"We lost Browny (Nathan Brown), obviously, pre-game, so we were pretty young back there. It would have been good to have him but we're optimistic that he'll be there."

St Kilda's forward line has been depleted by injury, with Josh Bruce out for the season with a broken fibula, while Josh Battle deals with a fractured right eye socket. 

Rookie Rowan Marshall looks set to return, having amassed 20 disposals, eight marks and three goals in the VFL's side draw with Coburg on Saturday.