The Dockers (17-2) have just three players on their injury list - only Jaeger O'Meara being a regular senior performer - ahead of Friday night's clash with the Western Bulldogs at Optus Stadium.
Contracted until the end of 2030, Darcy has overcome his own injury issues to be fit-again.
But he is being kept in the Dockers' WAFL team, Peel Thunder, due to the serviceable form of Magpies premiership player Cox.
Darcy had 23 possessions and 39 hitouts for the Thunder last week.
"There's a few things he's working on," coach Justin Longmuir told reporters on Wednesday.
"His stat line was impressive but there is work to do with some of the things he's been working on.
"Coxy will hold his spot. I've been happy with the way he's been able to go forward and give us an aerial contest.
"He's started sticking his marks and some of his ruck craft and the difference he brings in the ruck compared to Jacko gives us an advantage so Sean will just have to be ready when his opportunity comes."
Another win in the final month will break Fremantle's record for the most in a home-and-away season.
The Dockers have been managing to win games with powerful second-half bursts, losing all five first-quarters since their bye.
"Over the course of the year we've been pretty good in first quarters, it's just dropped away, our intensity and method," Longmuir said.
"It's our method a little bit, not just clearance but all over the ground.Â
"It doesn't take a lot and your opposition will get ascendancy in the game."
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