A North spokesman told AFL.com.au McMahon was awaiting the results of scans, but the club remained "pretty hopeful" he would play against the Dockers.
McMahon was placed in a moon boot soon after injuring his ankle.
Leading sports medico Dr Peter Larkins said McMahon's chances of playing against Fremantle would not be helped by North having to fly to Perth for the game.
"Routinely, people suffer swelling in the legs and ankles because of the cabin pressure during flights," Larkins said.
"So unless it's a really minor injury I suspect North would be concerned that the trip to Perth would just make McMahon's ankle flare up even more and err on the side of caution and leave him home."
McMahon would be a big loss to North's team if ruled out.
The 27-year-old has become a leader in defence in recent years, with the Roos winning just two of the six games he missed through a severe virus early last season.
Nick Bowen covers North Melbourne news for AFL.com.au. Follow him on Twitter: @AFL_Nick
