North Melbourne is not concerned that free agent Robbie Tarrant remains unsigned and believes the key defender wants to remain at Arden Street beyond 2015, coach Brad Scott says.

Tarrant is set to become an unrestricted free agent at the end of this season and has attracted significant interest among rival clubs, with Hawthorn and Fremantle understood to be leading the chase.

The former key forward has become a hot property after moving into defence this season and holding his own against star power forwards including Travis Cloke, Jarryd Roughead and Tom Hawkins.

But Scott told reporters on Thursday that the 26-year-old, who had played just 39 games in seven injury-plagued seasons before this year, remained a player the Roos were determined to keep.

"We've got really good people who take care of all that sort of (contractual) stuff," Scott said.

"Robbie's a really valuable member of our club. He knows that and he's really keen to stay with us.

"It's just a matter of those guys nutting out a deal."

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Scott said Shaun Higgins (knee) and Ben Brown (corked calf) remained in doubt for North's clash with St Kilda at Blundstone Arena on Saturday, but veteran defender Michael Firrito will come straight back into the Roos' side after serving a one-match suspension.

Higgins has been carrying knee soreness in recent weeks and had scans earlier this week.

But the former Bulldog looked to move freely in some run-throughs ahead of North's main training session on Thursday and Scott said he would play against the Saints provided he did not pull up sore.

"He's been dealing with this for a little while now. He'll do a really light session today and we'll see how he pulls up," Scott said.

"It will be a no-risk approach. If he's close to 100 per cent, he'll play."

Brown has been medically cleared to play against St Kilda, but Scott said the key forward would be monitored closely at Thursday training before a final decision was made.

Daniel Wells moved smoothly in three-quarter pace run-throughs on Thursday as he continued his bid to return before the end of the season.

The star midfielder has been sidelined by an Achilles tendon injury since he was substituted out of North's round two win over the Brisbane Lions at half-time.

"He's progressing," Scott said when asked for an update on Wells.

"We acknowledge we're running out of time, but we still maintain that he'll play again this season."

Meanwhile, utility Jamie Macmillan is set to miss at least another week as he recovers from the hamstring injury he suffered against Essendon in round 16.

"He's probably medically available but we just want to take a cautious approach," Scott said.