A worse-than-expected knee injury to midfield star Tom Scully has put a further wobble in Melbourne's bid for AFL finals for the first time in five years.

Scully will miss four weeks after soreness in his left knee was diagnosed on Wednesday as bone stress in his patella.

The No.1 draft pick's demise adds to a welter of injury problems for the Demons going into their season opener against Sydney at the MCG on Sunday.

Already with an injury doubt over highly-rated Jack Trengove, Melbourne have also lost tough-tackling youngster Jordie McKenzie for several weeks.

McKenzie has a groin problem and has been ruled out for at least six weeks.

Trengove faces a late week fitness test on an ankle problem, and the Demons are already without key defender James Frawley and Cale Morton through injury.

Melbourne doctor Andrew Daff said rest was vital for both Scully and McKenzie.

"The best course of action is for Tom to undergo a period of rehabilitation while resting from football loads," Daff said.

"We are hopeful that he can return to play in the next four weeks.

"Jordie has experienced an increase in groin pain due to pubic overload syndrome."

Should Trengove fail to play, it would leave the Demons relying heavily on experienced onballers Brent Moloney, Nathan Jones and Colin Sylvia.

Frawley, who has a torn pectoral muscle, and Morton, who has a hand injury, are a fortnight away from resuming.

Rookie-listed ruckman Robert Campbell (Achilles) is also at least six weeks away from playing.

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