The AFL has issued a 'please explain' to Port Adelaide over the club's handling of an apparent head knock to star defender Aliir Aliir on Saturday.

Aliir appeared to clash heads with teammate Lachie Jones in Port's loss to the Crows on the weekend, but while Jones was subbed out after undergoing a concussion test, Aliir did not undertake a SCAT5 concussion test, and played out the game.

Both Jones and Aliir have now entered concussion protocols and will miss Port Adelaide's clash with Geelong on Saturday night.

"In absence of the SCAT5 test occurring and out of an abundance of caution, the Port Adelaide Football Club has decided to enter Aliir into AFL concussion protocols and he will be unable to participate, at a minimum, in the club's round 21 match this week against the Geelong Cats," the AFL said.

"Upon further review after being substituted on Saturday night ... Jones, who was involved in the collision with Aliir, has also entered AFL concussion protocols.

"Both players will now need to undertake and medically pass the mandatory 11-step, minimum 12-day process before returning to play. The AFL's chief medical officer, Dr Michael Makdissi, will continue to liaise with Port Adelaide club doctors in the monitoring both players' progress."

Port Adelaide club doctor Mark Fisher said Aliir should have undergone a SCAT5 scan upon further review.

"Lachie was tested during the game and after it, then again on Sunday. We have continued to monitor him and after further testing this morning he has entered the concussion protocols out of an abundance of caution," Fisher said.

"Like Lachie, Aliir's condition was the subject of testing both on Saturday night after the game and since.

"However, upon reviewing the vision of the incident again, Aliir should have undergone SCAT testing at the time immediately following the collision.

"Both Lachie and Aliir will have a gradual return to play as per the AFL's concussion management guidelines."