Hayden Ballantyne needs hamstring surgery and will miss up to 10 weeks in a significant blow for Fremantle.
Scans revealed the 29-year-old would need an operation to repair tendon damage in his left hamstring.
Ballantyne tore his hamstring midway through the third quarter of Friday night’s 21-point JLT Community Series win over Carlton at Domain Stadium.
Scans were reviewed by a specialist this morning, who confirmed surgery would be required.
The seriousness of the injury represents a double blow for Fremantle, with forward Michael Apeness tearing the posterior cruciate ligament in his left knee playing in a practice match for Peel on Saturday.
Apeness, 22, will miss up to eight weeks with the injury.
Ballantyne is not expected to be available until at last round seven, effectively ruling him out for the first third of the home-and-away season.
“At this stage the medical advice is that Hayden will require a rehabilitation phase of eight to 10 weeks,” Fremantle football manager Chris Bond said.
“Once the rehabilitation process is completed and given Hayden’s strong pre-season, we expect him to make a significant contribution on his return to football.”
Apeness does not require surgery, but will be forced to wear a brace on the knee while he recovers.
It is a major setback for the key forward, who missed most of the 2015 season with a similar injury.