NORTH MELBOURNE has a message for the AFL when it comes to an ongoing investigation into the club's medical department, "get on with it."

Lachie Hansen - the player whose welfare is central to the inquiry - suffered another head knock on the weekend against GWS, but has been cleared to travel to face West Coast in a cut-throat preliminary final.

Fellow forward Drew Petrie told AFL.com.au on Thursday the unfinished inquiry was casting an unfair shadow over Kangaroos medicos.

"They just need to tidy up their investigation and get on with it," he said. 

"They've interviewed the doc, they've interviewed players, they've interviewed myself, I'm not sure where else they're digging, what angle they're digging for.

"I can understand why the AFL's doing it, but at the same time they are sort of questioning our doctor's ability to perform his duties, so that's a bit of a backhand slap in the face."

An AFL spokesman said the investigation was "ongoing" but would not elaborate on its length.

It's not the only inquiry the Kangaroos are facing from League headquarters, with coach Brad Scott yet to hear if he'll face punishment for his on-field spray at Giants playing-assistant coach James McDonald.

The AFL has confirmed a letter was sent to North Melbourne seeking an explanation, and it had yet to conclude the matter.

Matt Thompson is a reporter for AFL Media. Follow him on Twitter @MattThompsonAFL