UNBEATABLE a fortnight ago, Melbourne is facing a mini mid-season crisis as Tom McDonald deals with a potentially serious foot injury.

The premiership forward was a late withdrawal from Saturday night's upset 12-point defeat against Sydney at the MCG.

McDonald absence was due to ankle soreness, but coach Simon Goodwin revealed there are major concerns around his Lisfranc joint.

That type of foot injury generally rules players out for an extended period, with star Geelong defender Tom Stewart missing last year's finals because of it.

“It’s looking more like a Lisfranc,” Goodwin told 3AW on Sunday. 

"Tom looks like missing a bit of footy and he’ll be sorely missed because he’s a really important player for us."

The Demons' loss against the Swans means it is the first time since 2020 they have gone down in consecutive games, after last week's defeat to Fremantle.

Ladder-leader Melbourne went into the round 11 contest with the Dockers on a 17-game winning streak and many experts had them pencilled in for back-to-back premiership cups.

Goodwin is not panicking, but knows there is plenty of work to do ahead of games against Collingwood and Brisbane.

"We had our standard chat, standard review, and it was pretty clear that it's welcome to the AFL season - it's a tough industry," Goodwin said on Saturday night.

"We need to keep finding ways to get better as a footy club, it's a long year, and just at the moment we're not at our best but that doesn't mean it's going to last forever, either.

"We played a good side in the Swans, they played a good brand of footy and full credit to them."

Much of the concern stems from key players being sore and others who are out-of-form.

All-Australian defender Steven May was badly missed against the Swans after sitting out due to the AFL's 12-day concussion protocols.

Fellow backman Harrison Petty copped hits to his ankle and shoulder after entering the match with knee soreness.

Ben Brown struggled through his third-straight match goalless but Goodwin is backing the premiership hero to return to his best.

In a bold move, Melbourne preferred to recall veteran utility Mitch Brown over promising tall forward Sam Weideman when McDonald was ruled out.

"I don't think anyone's guaranteed a run in the AFL, everyone earns their position," Goodwin said.

"There's no doubt it's competitive with our key forwards for spots.

"Ben's not at his best at the moment but he's a very good player. Our challenge as a coaching group is to get him back into form.

"(Weideman's) got to keep working hard on his game, continually be working on playing a big man's type of footy.

"He'll have a good look at opportunities throughout the year but at the moment Mitch Brown is just playing better."

Weideman booted three first-half goals in the Casey Demons' VFL win over Sydney on Saturday afternoon, and finished with 12 disposals and 10 marks.