INJURED North Melbourne vice-captain Jack Ziebell is in serious doubt for this Sunday's clash against Port Adelaide, with Roos coach Brad Scott suggesting he might have to protect the courageous midfielder from himself.

Ziebell did not take part in North's main training session at Arden Street on Thursday after injuring his shoulder in an attempted spoil on Western Bulldog Easton Wood early in last Sunday's game.

Scott said North could delay making a call on Ziebell's fitness until as late as Sunday morning.

Ziebell was cleared of structural damage on Monday after scans and a visit to a surgeon, but Scott stressed North would take a safety-first approach.

"We'll name him in the side but only because we want to give him right up until the last minute," Scott said on Thursday.

"I've got to work out whether he's his own worst enemy and goes out and hurts himself again.

"Even though structurally there's no risk, the way he plays if he gets another serious hit on it, it's clearly going to be sore.

"We certainly don't want it costing us the game because we've got a player injured early in the game."

Twitter: @AFL_Nick