The ladder-leading Dockers will start as hot favourites against injury-ravaged Port Adelaide at Adelaide Oval on Saturday, but the loss of Bolton came as a surprise.
The former Tiger has been managing a minor hand injury in recent weeks, but wasn't named on the club's injury list on Tuesday.
Coach Justin Longmuir refused to confirm or deny Bolton's absence was due to the hand niggle, but said the injury wasn't serious.
Bolton will be replaced in the side by fit-again midfielder Hayden Young (groin).
"He's dealing with an injury that would do with a week off," Longmuir said of Bolton.Â
"It's not serious, so it's probably a one weeker. But yeah it's a good opportunity to manage him and Hayden will come in and play a similar role to what Bolts has been playing."
Premiership ruckman Mason Cox will hold his spot ahead of Darcy after producing an eye-catching display in last week's 38-point win over Sydney.
Cox tallied 10 disposals, 10 hitouts, six marks and one goal as Luke Jackson's back-up ruckman, and the former Pie will notch his 150-game AFL milestone when he lines up against Port.
Darcy was rested from the Sydney clash due to it coming off a five-day break and now he faces a fight to win back his spot in time for finals.
"I've spoken to Sean. He's disappointed," Longmuir said.
"When we managed him last week I told him there were no guarantees, and Mason's come out and played really well.
"Sean ... his form's not quite where we need it to be."
Darcy has been plagued by injuries in recent years and the new ruck rules that favour more athletic big men haven't helped his cause.
The path for Darcy back in the senior side is less about dominating in the WAFL and more about improving his athleticism.
"We've done a lot of work behind the scenes with Sean just to get his mobility going," Longmuir said.
"He's clearly missed a lot of footy. He's been working through that knee injury that he had last pre-season and just doing some work behind the scenes with his footwork and ruck craft.
"It's more about what he can do athletically to lift his athletic profile in some sense and he's working really hard behind the scenes to do that."
The Dockers (15-2) are two games clear of second-placed Sydney, but Longmuir says he will only rest players if they really need it.
"Sometimes with some niggles, it's better off to keep them playing," Longmuir said.
Port (6-11) will be without Zak Butters (ankle), Mitch Georgiades (concussion), Jason Horne-Francis (suspension) and Jack Lukosius (knee).
