Coach Ross Lyon could not confirm the knee injury to ruckman Jon Griffin as a ruptured ACL but he said the early prognosis was not good.
"Look, [we have] grave concerns," Lyon said.
"But those grave concerns need to be legitimised with scans and orthopaedic surgeons who are really accurate in their assessments."
Griffin is the latest addition to a long casualty list at Fremantle.
Kepler Bradley has already been lost for the season with a knee reconstruction, while Stephen Hill missed a second week with a quad injury.
Matthew Pavlich is still two to three weeks from returning and Aaron Sandilands and Anthony Morabito are even further away.
"It puts us under some pressure," Lyon said of the growing injury toll.
"We've had some unfortunate stuff, but that's AFL footy. It's a hard environment."
Lyon felt there was a point at which a critical mass of injuries could render a team's season terminal but he said Fremantle wasn't there yet.
"I think we've all got our common sense hat on. I think there's a tipping point.
"There's not a formula for it. It would be nice to not get any more though.
"At the end of the day we've still got some talent to come through.
"We're not on our knees yet."
The impending returns of Nathan Fyfe from suspension and Hill from his quad injury are positives for the Dockers ahead of their clash with the Sydney Swans on Saturday night.
Lyon also mentioned the good form of Viv Michie, Tom Sheridan, and Jesse Crichton in the WAFL.
But it is the big man department that is alarmingly thin.
With Aaron Sandilands still six weeks away, the ruck duties will be left to three-gamer Jack Hannath - who acquitted himself well against Collingwood - and Zac Clarke, who is due to return from a calf problem.
However, Lyon said Clarke was no certainty to come back as he had not played in the WAFL.
"He's available, he trained this morning. He needs to stand up," Lyon said.
"I saw him in the race on the way in, and I said 'you need to stand up'. He gets an opportunity.
"When that is, I'm not sure."
If Clarke is not called up, defender Zac Dawson may be the back-up for the inexperienced Hannath having filled the role against the Pies after Griffin went down.
"I know he can ruck, he's rucked before. I thought he was terrific," Lyon said.
"That's what we do know about Zac, he'll compete."
