Fremantle confirmed scans revealed a new fracture in captain Alex Pearce's left forearm that occurred during Sunday's 50-point win over Melbourne.
Pearce was cleared to return after fracturing the same bone against Gold Coast in Round 15, coming back with a protective armguard.
It was to no avail and the club has yet to give a timeline on his return date.
“Unfortunately, Alex has suffered another fracture of his left radius after an incident in the third quarter against Melbourne,” said Dockers Football Manager Joe Brierty.
“It's really disappointing for Alex who made such a strong return in the opening three quarters of the game.
“Our medical team will now consult specialists to consider the best intervention in collaboration with Alex and we will then have a better understanding of Alex's return to play timeline.”
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Pearce will now be in a race to return before the end of the home-and-away season, as the competition heads into the final five weeks of the regular campaign.
The Dockers' emphatic victory over the Demons pushes them into the top four, with a keen eye on a home Qualifying Final.
Fremantle coach Justin Longmuir said post-game that young defender Josh Draper is likely to get the nod to replace Pearce.
"It's sore. The game was done, so we thought we'd sub him off. He has to get a scan and we'll go from there," Longmuir said.
"(Pearce is) probably a little bit nervous (and) he's a little bit frustrated.
"Being the captain of the club and being in such good form all year, he wants to be out there competing with his brothers.
"Draper's is in good form and he's played a lot of footy. If he gets another opportunity, I'm sure he'll be ready to take it."
Fremantle will turn its attention to the Western Derby when they face arch-rivals West Coast on Saturday.