Jack Ziebell has to pass a fitness test on Friday before he is cleared for the still "formidable" task of playing the weakened Cats in Geelong on Sunday, North Melbourne coach Brad Scott says.

Ziebell coughed up blood and spent two nights in hospital battling bruised lungs after a heavy collision with Port Adelaide's Ollie Wines during the first quarter of the Kangaroos' nail-biting eight-point loss last Saturday night.

But the tough midfielder is pressing his claims to play at Simonds Stadium this Sunday.

Scott said Ziebell would have to pass a series of tests under the watchful eye of North's doctors and physios.

"He's actually feeling terrific. He feels like he could play today, but we've got make sure his lung function's right and there's no risk," Scott said on Thursday.

"So there's some pretty specific physiological tests that he's got to undertake.

"It's going to be really cut and dried, I think. This is not going to be one where we think, 'Maybe he could, maybe he couldn't'. He'll either be right or he won't.

"We'll give him every opportunity and the way he's recovered we're really optimistic."

PRESS PLAY above to watch the Brad Scott media conference | YouTube

Scott said Ziebell would be named in North's extended squad if he passed some "very small steps" at Thursday's main training session.

Star onballer Daniel Wells (Achilles) trained lightly on Thursday, but is also facing a fitness test after he was a late withdrawal from the Power clash.

Scott said defender Jamie Macmillan, who has missed the past two games with an Achilles issue, was also in contention.

"We think he'll be fine, but you've mentioned three guys there so we've got to make sure that they're right," he said.

"We're not going to take guys in who are not quite right and take a risk."

While the Roos could regain the important trio, the Cats will be without Jimmy Bartel (knee), Mathew Stokes (Achilles) and Andrew Mackie (quad).

Key defender Tom Lonergan (concussion) could also miss the vital game, which both sides – widely tipped to finish in the top eight - enter on one win and two losses.

While some viewed Geelong's battling win over Gold Coast at home last Sunday as a sign of the club's demise, Scott retains the utmost respect for the Cats.

He said it remained a significant challenge taking on the Cats on their home turf – where North has lost eight of its past nine stretching back to round five, 2007.

"I watched the game last week…I wouldn't think that playing Geelong this week we'd have any more confidence than any other week," Scott said.

"That win against Gold Coast was full of merit and it was full of courage and it was full of character.

"I think Geelong, the discussions around their death have been premature. They're still a very formidable side with formidable players.

"More importantly they're a club with great character and great pride, so we expect a very, very fierce contest."