Young Demons ruckman Luke Jackson has gone down with a hamstring injury at training.

It's a cruel blow for the club, with skipper Max Gawn already racing against the clock to be fit to face Collingwood on Saturday.

Gawn has been battling a shoulder injury along with managing a knee injury.

Seven News' Tom Browne reports Jackson's injury is suspected to be on the serious side.

“A significant hamstring injury could keep Jackson out for the rest of the season given the AFL’s fixture squeeze will continue through to the start of the finals.”

With Gawn struggling with fitness and now Jackson out, Dees coach Simon Goodwin has a tough selection call ahead of him.

He could be forced to call on reserve ruckman Braydon Preuss for the first time this season.

Preuss played seven games last year, averaging nine touches and 19 hit outs.

Gawn has a fitness test ahead of Saturday's clash with the Pies, according to vice-captain Jack Viney.

“I know he’s pretty aggressive with his injuries,” Viney told 7NEWS.

“But if we miss Maxy it’s going to be a bit of a shame, he’s such a special player for us.”