Port Adelaide key forward Todd Marshall has been devastatingly ruled out of next week's preliminary final against Sydney at the SCG.

The 25-year-old had just re-joined the side following a one-game-in-eight-weeks absence due to a hip injury.

He was sidelined for a large portion of the second term in Friday night's semi-final victory after sustaining a knock to the back of the head.

Cleared to continue on after half-time following a second quarter HIA, Marshall played out the remainder of the win, though failed a secondary test in the aftermath.

Speaking to reporters on Saturday afternoon, Power CEO Matthew Richardson spoke on the concerns surrounding Marshall's health but played down concerns the latest head knock could place questions around his future following a history of head trauma for the Port Adelaide tall.

"It's certainly too early for that. Clearly it's concerning. We always take a really cautious approach with these things," the Power boss said.

"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."

Initially prepped to play with all three key forwards Mitch Georgiades, Todd Marshall and Charlie Dixon, Ken Hinkley and the Power were left depleted in the tall forward stocks and will be again in their fight for a grand final berth.

Dixon is likely to return after being ruled out due to illness, but is clearly a mobility concern against Sydney's dashing defenders.

Without Marshall, the bulk of the load will be put on 22-year-old Mitch Georgiades to lead Port Adelaide's forward crop to what would be the greatest win of Hinkley's tenure.