Scans on Monday confirmed Fyfe suffered a "moderate grade" hamstring strain while playing for WAFL affiliate Peel Thunder on the weekend.
The 33-year-old lasted less than one quarter of the match, pulling up sore after attempting to lay a tackle.
He will not require surgery, but will be monitored over the next fortnight before the Dockers finalise his return-to-play timeline.
Fyfe had arthroscopic knee surgery in January and battled ongoing soreness before his WAFL return was cut short.
"It's really disappointing for Nat. He's worked so hard to get back," Pearce told AAP.
"Our whole club's right behind him and we hope it's nothing major and we'll get him back soon."
Fyfe's latest setback raised fears the dual Brownlow medallist could be set to announce an early retirement.
The 240-game veteran is out of contract at the end of this season.
But Pearce joined Dockers coach Justin Longmuir in dismissing those suggestions.
Pearce backed Fyfe to return and have an impact as Fremantle press for a finals berth.
"Absolutely he can. If he sets his mind to it, he'll get it done.," Pearce said.
"If there's a chance that his body allows him to, then he'll do it. That's the type of bloke he is."
The Dockers (3-2) are riding a three-match winning streak into a clash with Melbourne at the MCG on Saturday.
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