Mackie has suffered hamstring soreness for the past two weeks and was subbed out of the Easter Monday win over Hawthorn at three-quarter time.
"He's got quite a complex issue with his hamstring," Cats coach Chris Scott said on Wednesday.
"It's really hard to describe. It's that sort of tendon issue. It's almost like a tendonitis sort of thing.
"He was right to play on the weekend, and did a really good job for us, but he's a genuine question mark for this week.
"He hasn’t done any more damage to it, but it has given us reason to think about how we manage him in the short-term."
As for whether Geelong will name Mackie in its side, Scott said. "It's a possibility. The way the system works, if you don't name a player he can't play.
"So we tend to name them if there's any chance that he will play and then leave our decision a little bit later."
The Cats could be boosted by the return of dynamic half-forward Steven Motlop, who is pushing strongly for a recall after impressing in the VFL last weekend.
Motlop has recovered from the knee issue that interrupted his pre-season, and he would seem perfectly suited to returning as a sub.
But Scott said: "Our position is that when he's ready to play AFL football, we'll need to be sure that he can play out the full game.
"Because even as the sub, you can get an injury in the first minute and he needs to have the capacity to play out the full game.
"Again, we're not going to risk it … he's either right to play as he normally would in an AFL game or he'll play modified game-time in the VFL."
Matching Port Adelaide's running power will be a challenge for Geelong on Sunday.
But resting one of the three ruckmen who have appeared in all five rounds so far does not appear to be on the agenda.
"Specifically, with our three ruckmen, we think one of them (Mark Blicavs) is the best runner in the comp," Scott said.
"So he's not limiting our running power by any stretch."
