GUN GEELONG defender Tom Stewart is set to undergo surgery after suffering a potentially season-ending foot injury.

Stewart sustained the injury in a marking contest at training on Thursday and has been reduced to a moon boot and crutches as he awaits further clarity. 

Coach Chris Scott confirmed the 28-year-old needs surgery after suffering Lisfranc (mid-foot) damage, which can typically rule players out for one to three months or longer if an operation is required.

Smooth-moving half-forward Sam Simpson replaced Stewart in the Cats' line-up which defeated St Kilda by 14 points at GMHBA Stadium on Saturday.

"He's going to have surgery on that Lisfranc ligament injury on Monday, so if people are saying he's going to be out for the season, they know more than I do," Scott said.

"I don't think even a higher power knows if he will come back or not, but what we've been told is that it's possible, however slim that chance is.

"Probably the last game of the season (Grand Final) is the hope, so we've got a bit of work to do between now and then.

"I don't often say this, but he's been our best player for the year. Often we look at players and reference the past and their reputations too much rather than looking at a season in isolation – if we do that, he's been superb for us."

The AFL has flagged the possibility of scrapping the pre-finals bye to continue with the momentum with the season due to the threat of COVID-19 which could further hamper Stewart's chances of a return. 

Mitch Duncan is already racing the clock to return with his PCL setback, while Zach Tuohy will miss at least the remainder of the home and away campaign with a hamstring strain.  

Scott said Gary Rohan is a "probable" chance to return next week against Melbourne, after missing the win over St Kilda with a hip issue.

However, Stewart has proven an incredible healer of injuries in his five-year AFL career that has already netted two Therabody AFL All-Australian blazers and is on track for a third. 

In 2017 he underwent surgery to repair a fractured eye socket that was initially expected to rule him out for four-to-six weeks before he missed just three matches. 

Last season he was also put under the knife for a broken collarbone and returned to play inside a month. 

Stewart has played 106 of a possible 114 games since his debut in the 2017 season opener.