And Dockers veteran Michael Walters has been forced to the sidelines again after his troublesome knee flared up after last Saturday's WAFL hit-out.
Darcy is contracted to Fremantle until the end of 2030, but Essendon are rumoured to be in the hunt for his services if they lose Sam Draper to Adelaide or the Brisbane Lions.
Fremantle's large investment in Jackson and Darcy as a two-man ruck combo has come under heavy criticism, especially in the wake of Darcy's injury struggles.
The 27-year-old has played just seven of the Dockers' 14 games this season, on the back of being restricted to 12 appearances in 2024 and 15 the previous year.
Jackson has thrived in the games Darcy has been absent, leading to calls for Fremantle to cut the dual ruck experiment short.
Dockers coach Justin Longmuir doesn't agree, and he'll unleash both Darcy and Jackson together in Sunday's clash with St Kilda at Optus Stadium.
Goalsneak Isaiah Dudley and defender Oscar McDonald also return for Fremantle (9-5), with Josh Draper, James Aish and Jeremy Sharp axed.
The set-up against the Kangaroos and Suns resulted in Jackson taking on the lead ruck role, as well as playing as a big-bodied midfielder or forward at times.
Darcy was a best-and-fairest winner in 2021 as one of the competition's premier ruckmen, but knee and soft-tissue injuries have halted his progress.
Longmuir wants to keep playing Darcy, but the 203cm ruckman will have to be content with a diminished role.
"While Sean is building form, he's happy to play whatever role the team asks of him," Longmuir said.
"He cops a little bit of a lower game time, but it's probably going to be the new way for him in some respects.
"That's probably more about his body than anything. He's been injured a lot."
Walters made his long-awaited comeback from knee surgery in the WAFL last week, but pulled up sore from the encounter.
"The way he described it to me was he took two steps forward to play a game last week, and he's probably just taken a step back," Longmuir said.
"He's got a bit of soreness in that knee again. I don't think it will cost him more than one week."
He said skipper Alex Pearce is on track to return for next week's crunch clash with Sydney at the SCG.
St Kilda (5-9) welcome back Liam Henry from injury, while Hugo Garcia and Jack Carroll were also recalled.
Brad Hill (illness), Jimmy Webster (managed) and Ryan Byrnes (omitted) go out of the side.
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