STAR Greater Western Sydney forward Jeremy Cameron has been ruled out for at least three weeks with a hamstring injury. 

It's a massive blow for GWS and if the club's best tall forward has any type of setback with his rehabilitation, Cameron won't play until the club's first final.

Cameron, who had missed the Giants' losses to Sydney and Richmond in rounds 17 and 18 with hamstring soreness, was recalled to the side last week but struggled through the second half against Fremantle.

The 24-year-old kicked one goal from 16 possessions in the 12-point win over the Dockers at Spotless Stadium, and after the match coach Leon Cameron told the media that his gun forward had copped a knock to his back in the first half.

GWS head of athletic performance David Joyce said on Monday scans had revealed Cameron had suffered a grade two hamstring strain but denied the forward had come back too early.

"There's no reason why he shouldn't have played the game, he was absolutely fine to go into the game," he said. 

"He couldn't have been more prepared. He wasn't rushed back, it was just one of those unfortunate things.

"He got a hit in his back in the second quarter and felt some symptoms down that leg. 

"He tested really well throughout the second half. We went out repeatedly just to check on him and he was fine. We specifically tested him at three-quarter time and he was fine.

"He actually presented worse post match so we scanned him and unfortunately it's revealed he's got a hamstring strain."

The Giants play Melbourne in Canberra this week, before finishing the season with three more tough games against the rejuvenated Western Bulldogs (away), West Coast (home), and fellow top four hopefuls Geelong (away).

Cameron is the only player to have won the Giants' leading goalkicker award and currently has 42 for the 2017 season, ahead of Jonathon Patton (36) and Toby Greene (33), with Patton the only player of that trio set to face the Demons with Greene serving the second week of his suspension.

Steve Johnson (knee) and Shane Mumford (ankle) will all be tested ahead of round 20 and could be recalled to face the Dees, with draftee Will Setterfield (concussion) also to be monitored after he copped a heavy knock against Fremantle.