Port Adelaide coach Matthew Primus says talented forward Robbie Gray will be tough to replace after going down with a suspected AFL season-ending knee injury.

Gray, the Power's leading goalkicker last season, had to be stretchered from the field less than a minute from fulltime of Saturday's loss to Collingwood at Etihad Stadium.

While Gray will be assessed on Monday, club medical staff were almost certain he tore his anterior cruciate ligament.

"It's not good news. Robbie's an important player to our future," Primus said, adding there was no comparable player ready to step up.

"He's different to anyone we've got, obviously.

"We've got some guys in the SANFL in some form.

"They're different to Robbie, but we'll find someone else to fill the breach.

"That's why we've worked hard in pre-season - to make sure we've got a squad that can step up when we need it."

Port's attack struggled on Saturday, as their attempt to exploit the Magpies' injury-depleted defence backfired.

With the Magpies missing tall defenders Ben Reid, Chris Tarrant and Nathan Brown, the Power lined up with big marking targets Jay Schulz, John Butcher, Daniel Stewart and Justin Westhoff all in attack.

But while that quartet failed to fire, the rebound Collingwood produced from defence proved a key weapon.

Primus said the bigger worry for him than the Magpies' run from the backline was the failure of his forwards to do much damage themselves.

"Our key guys weren't able to mark it, that's what I was more concerned about," Primus said.

"Schulzy took four or five marks, Daniel Stewart took a couple, Butcher didn't take many, Westy didn't take many as a forward.

"We were looking for them to mark the ball."