The Power are reeling from a fourth straight loss, this time a 12-point defeat to Geelong on Saturday night, in a slide that has put their top-two hopes in jeopardy.
The latest setback came as McKenzie was substituted out with a right knee injury.
"It's probably a PCL (posterior cruciate ligament) but we won't know until we do the scans," Power coach Ken Hinkley said post-match at GMHBA Stadium.
"But it looked and acted like a PCL, so that'll be a medium to long-term recovery, and that will be a bit of a challenge for us."
Port were struck by illness ahead of the Geelong clash, with Jeremy Finlayson and Miles Bergman late withdrawals before the first bounce after Kane Farrell was ruled out on Friday.
Those blows came with Aliir Aliir and Lachie Jones already unavailable under concussion protocols, and key forward Charlie Dixon (foot) pulled out of the selected side.
Hinkley is hopeful most, if not all, of those six will return against the Giants at Adelaide Oval in round 22.
"I'd imagine there's a minimum of five, maybe Charlie, but his injury this week was a little unusual the way it appeared late in the week," Hinkley said.
"We'll wait and see what that looks like."
Hinkley isn't ready to hit the panic button despite the four-match losing streak casting serious doubt over the Power's premiership credentials.
The dip in form has come after a club-record 13-match winning streak.
"I think we're ok. We're thereabouts," Hinkley said.
"We were poor last week (against Adelaide) but either side of that we've played Collingwood and Geelong and we played pretty well in both those games without getting a win.
"Ultimately, we set our season up pretty strongly with the run that we got on and now we've got to reverse a little bit.
"But I'm still confident that we're a pretty good team."
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