Powell-Pepper will have scans on his knee after going off during the third quarter of Port's 11.16 (82) to 10.12 (72) win over St Kilda at the Adelaide Oval on Friday night.
It was a night of carnage for the Power, who also lost captain Connor Rozee (hamstring) and defender Aliir Aliir (concussion).
Powell-Pepper after going down with what Hinkley called a "nasty" injury. (Matt Turner/AAP PHOTOS)
All three will almost certainly miss Port's Showdown against Adelaide back at the same venue on Thursday night.
Port coach Ken Hinkley admitted the incident looked "a bit nasty".
"The medical report is that they're a little bit hopeful," he said.
"But we'll wait and see what, again, what the scan says.
"There's some scare because he's hurt his knee.
"When you hurt your knee, and can't go back on, my history in the game and the amount of times I've seen those sort of things happen, it lends itself towards possibly being an ACL.
"But the doctors were saying afterwards, that there's some promising parts around the way it tested. We won't guess, it's too hard to guess."
Powell-Pepper was only playing his third game since serving a four-match suspension for a high bump during a pre-season hitout.
Rozee, Port's star midfielder, will likely be sidelined for Port's first home-and-away opportunity to play their cross-town rivals, the Crows, since he was named captain ahead of this season.
The 24-year-old will undergo scans but indicated in a post-game interview it was a minor hamstring strain.
"Just a little nick in the hammy so hopefully not too long," Rozee told the Seven Network.
Aliir has been placed into concussion protocols following a tackle by St Kilda small forward Jack Higgins in in the second term.
Higgins faces a nervous wait to learn if he will be cited by the match review officer for a dangerous tackle.
St Kilda coach Ross Lyon said he had not seen the incident
"There's great processes and structures within the AFL and the game so everything gets taken care of in the end," Lyon said.
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