Port Adelaide's Lindsay Thomas is facing a possible suspension after he was placed on report for high contact during the Power's 34-point AFL loss to Geelong.
Former North Melbourne player Thomas made contact with Scott Selwood, leaving the Cats midfielder concussed and unable to play the rest of the game.
Thomas will likely be sent back to the sidelines for the bump, which happened midway through the second quarter just minutes after he kicked his first goal for the Power.
The 30-year-old was brought into the side at the last minute after Todd Marshall failed to recover in time following a concussion last week.
Power coach Ken Hinkley said the collision was "ferocious" but unintentional.
"No player goes out there deliberately to try and cause things to go wrong, but in a contact sport, they do happen that way," he said.
"From our point of view, Lindsay was trying to do the right thing."
Cats coach Chris Scott said, in general, the game had done a good job of stamping out such incidents.
In this case, he said, Selwood was "a sick boy" and described the bump as serious.
"It was pretty clear right away that he wouldn't be able to come back," he said.
"I've said this a number of times, with issues like this, they can seem really innocuous and players miss weeks, and the ones that look really serious, they're right in a few days."
He said it was not yet clear whether Selwood will recover for Geelong's clash with Sydney next weekend.
Port Adelaide's Hamish Hartlett left the ground on a stretcher after a collision with Geelong's Patrick Dangerfield, also during the second quarter, but passed a concussion test and returned for the second half.