STAR Hawthorn forward Jack Gunston faces an interrupted preparation for this year's finals series after the news he will miss up to three weeks with a knee injury. 

Scans revealed Gunston suffered the medial ligament injury when a Western Bulldogs opponent fell across him in the final quarter of the Hawks' 62-point win on Sunday. 

Although the club's football operations manager Chris Fagan said the damage was "low-grade", Gunston may only play one more game for the home and away season before September action.

Gunston, who has kicked 44 goals this season, will be missing for at least the Hawks' meeting with Melbourne on Saturday, and the round 21 clash with Fremantle in Perth.

He is in doubt for the blockbuster against Geelong in round 22, but the club hopes he will be fit to face the Magpies in round 23. 

"You'd expect at the very latest he'll be OK for the Collingwood game," Fagan told the club's website.

"Jack has had a full season so we think he'll make a pretty quick recovery and be on the go for the finals."

Sam Mitchell is expected to return against the Demons after being a late withdrawal against the Bulldogs with illness, while the Hawks were cautious with Isaac Smith, who was another late out with calf tightness. 

"We made the call not to take the risk with [Smith]," Fagan said.

"The expectation is he'll train this week and be available against Melbourne."

Veteran midfielder Brad Sewell, who injured his hamstring against North Melbourne in round 16, is also likely to be available this weekend. 

The 30-year-old has played seven games this season for a total of 197 for the Hawks.