Clarke hasn't played since injuring his calf in the WAFL seven weeks ago, and coach Ross Lyon was eager to give the 23-year-old one or two runs in the reserves before handing him a senior recall.
But with Jon Griffin and Kepler Bradley ruled out for the season with knee injuries, and No.1 ruckman Aaron Sandilands (hamstring) still at least five weeks away from resuming, Fremantle opted to give Clarke an earlier-than-planned recall.
Lyon was confident Clarke's superior aerobic ability would hold him in good stead despite the lack of match practice.
"He's done an enormous amount of training," Lyon said on Thursday.
"We know he's a gifted runner. We know he can handle up around 90 per cent (of game time), so that will be the aim.
"If it doesn't work we can always sub him out and bring on a runner."
Clarke has played in the shadow of Sandilands for much of his 36-game career, but now has the chance to cement himself as a frontline ruckman.
"Like any player he'll relish the opportunity. If you don't relish that opportunity you're in the wrong business," Lyon said of the 203cm Docker, who has also spent time on the wing and up forward.
"There's some pressure to perform but it is on the whole club to keep performing and we understand that.
"It's not all going to happen in one game for Zac. We just want him to compete and give a really good effort."
Fremantle have been bolstered by the return of midfielder Nat Fyfe from suspension, but the Dockers will still enter the match as underdogs given Sydney's prowess at the SCG.
