PORT Adelaide's defensive woes look to have deepened with Trent McKenzie and Dylan Williams in grave doubt for next week's semi-final against Greater Western Sydney.

In a chaotic third quarter against Brisbane on Saturday night, not only did Port concede eight goals to watch the qualifying final drift away, but McKenzie (ankle) and Williams (hamstring) left the field.

And all this came just minutes after coach Ken Hinkley made a tactical substitution by replacing Darcy Byrne-Jones with Travis Boak, leaving him short on the interchange bench.

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While McKenzie returned to try and give his "badly rolled ankle" one last go, the veteran defender eventually succumbed in the final term and was taken off for good.

Port was already struggling to contain Brisbane when its defensive stocks were thinned, but that was the final nail in the coffin as Joe Daniher (five goals) and Cam Rayner (three goals) led the powerful Lions' attack to victory.

Following the 48-point loss, Hinkley said McKenzie would be given every chance to line up against the Giants next weekend.

"We'll take the load off that ankle straight away, so you'll see him on crutches … you shouldn't panic about that," Hinkley said.

"He'll need every minute of next week to be available, and I think that's reality."

Port's coach seemed even less optimistic about Williams, saying his hamstring would be scanned before making any final decision.

All this comes just two days after captain Tom Jonas suffered a calf injury at training on Thursday, ruling him out for two to three weeks.

Despite some potential selection headaches ahead of facing the Giants, Hinkley was pragmatic about his team's chances of progressing to a preliminary final.

"We'll have to do with what we have available and I'm optimistic that's still strong enough and good enough, I don't think that's a problem," he said.

"We'll be OK. We earnt the opportunity to play again, worked really hard all year to get that opportunity.

"Obviously we would have preferred to not use it, but we now get to use it and we'll be ready to go and looking forward to the opportunity to play.

"We played GWS at Adelaide Oval not that long ago and we had a nice strong win."

Hinkley said the early goalkicking yips against Brisbane, highlighted by three easy misses by the usually reliable Todd Marshall, was a factor in the game, but certainly didn't decide it.

He was more concerned by the Lions' heavy scoring from clearances, from where they managed to pile on 13 goals.

"We lacked some composure, we lacked some ball use at times in that first half, but to their credit when they overpowered us, they really overpowered us.

"They were just better."

Full-forward Charlie Dixon is a chance of returning from a foot injury next week, with Hinkley saying he was "in the optimistic basket, but not necessarily in the team".