The veteran Fyfe is currently battling a stress fracture in his foot after suffering a setback against the Western Bulldogs in Round 16, while Darcy, a physical specimen in the middle of the ground, won't play again this year due to a bothersome ankle injury.
Fremantle high-performance expert Phil Merriman explained Fyfe will undergo surgery to repair two issues, consequently putting an end to his 2023 campaign.
"Nat's foot recovery has been a little bit slower than first expected so we've taken the option of ruling him out for the rest of the season," Merriman said on Monday.
"Nat will also go in and have a little bit of work done on one of his fingers, which was always the plan towards the end of the year."
Meanwhile, regarding Darcy, Merriman said the decision was made by the Dockers' medical team to fix the ailment via season-ending surgery.
"Sean's gone through the specialist process and we've made the decision to take Sean out and put him into surgery, so he'll be out for the rest of the season," Merriman added.
As the Dockers prepare for a Round 20 clash with Geelong at GMHBA Stadium, forward Bailey Banfield (knee laceration) and wingmen James Aish (quad) and Nathan O'Driscoll (calf) are tests to play against the Cats.
"They're progressing really well. They've got a few more boxes to tick towards the end of the week but we're hoping they'll be available," said Merriman.
Fremantle's meeting with Geelong is fixtured for Saturday, July 29 at 1:45 PMM (AEST).