PORT Adelaide forward Todd Marshall will miss the Power's preliminary final against Sydney after entering concussion protocols.

Marshall copped a knock in the second term of Friday night's three-point semi-final win over Hawthorn.

The 25-year-old underwent a head injury assessment at the time, which he passed, and played out the game.

But Marshall failed a secondary test post-game and is subsequently ruled out of next week's final.

The semi-final was Marshall's first game since being concussed and substituted out of the round 23 game against Melbourne on August 10.

That concussion was Marshall's fifth in a three-year period - last season he was concussed twice in a month.

Port Adelaide chief executive Matthew Richardson says it's premature to declare Marshall's career is endangered.

"It's certainly too early for that," Richardson told reporters on Saturday.

"Clearly it's concerning. We always take a really cautious approach with these things.

"I'm disappointed for Todd, I thought he was terrific early last night as well and played a really important role.

"Our medical guys will do everything they can to make sure we look after his health and wellbeing."

Marshall booted one goal from his five disposals in Port's memorable semi-final win. The Power will now travel to play Sydney at the SCG for a place in this year's Grand Final.

The Power survived a late Hawthorn charge to secure one of the club's great finals wins, booking their preliminary final spot against Sydney.

They held firm in some desperate final moments after Hawthorn skipper James Sicily hit the post with a long-range set shot that would have given his team a two-point lead, with Esava Ratugolea intercepting a final flurry forward from the Hawks.

It came after a week of fierce criticism following Port's 84-point belting at the hands of Geelong a week earlier.