North Melbourne entered this pre-season with a large rehabilitation group after a horror run of bone-related injuries in 2014, but the Roos' playing list is suddenly looking a lot healthier.

Although North announced this week Aaron Mullett had undergone shoulder surgery that would sideline him until mid-May, the Roos have been boosted by the recent returns of Drew Petrie (ankle), Aaron Black (shoulder), Robbie Tarrant (tibia stress fracture), Nathan Grima (foot) and Leigh Adams (knee) to game-sense training.

North high performance director Steve Saunders told AFL.com.au on Thursday that he expected Ben Brown (knee) and Majak Daw (dislocated foot) would also start game-sense training next week, while star defender Scott Thompson would join them a week or two later after having minor knee surgery over the Christmas break.

"Last season we had our worst season for injuries ever; we lost 100 games due to bone injuries," Saunders said.

"So off the back of broken bones and grotty joints and things like that, we've had a few things to deal with in the off-season.

"The rehab group has been large and definitely bigger than last year.

"But things are starting to look up and the late start to the season has come at a really good time for us."

The Roos' remaining rehab group members include Lindsay Thomas (foot), Lachlan Hansen (hips), Kieran Harper (ankle) and Taylor Garner (hip).

Saunders said Hansen was the least advanced in his pre-season campaign, with the key defender still four to six weeks away from re-joining North's main training group.

"He had surgery on both hips; one required a little bit more work than the other," Saunders said.

"He's still got some basic conditioning and strengthening to do before we really want to press that hip.

"He's running and doing all of his strength work, but we just can't progress it too quickly."

Saunders said Thomas had "come along beautifully" over the past month after needing an extended rest to recover from a plantar fascia injury he carried through the latter part of 2014, but was still about three weeks away from returning to full training.

The Roos' high performance director expects Harper and Garner will return to the main group within a month, with Harper far more advanced in his training than at this time last year.

Steve saunders on:

Scott Thompson
"He had some minor pain at the back of his knee throughout last season, which persisted through the pre-season despite some interventions, some strengthening and some rehab. So we needed to go in and deal with that over the Christmas break and he's looking really good now."

Jack Ziebell
"Jack needed some pretty complex shoulder surgery so we've had to hold him back in terms of contact work. But it's given us an opportunity to work on a whole bunch of other things that are probably more important to Jack than contested ball work, and he's actually moving better than we've ever seen him move before."

Kieran Harper
"He's had to do a lot of work on getting the (ankle) joint stable and the muscles around it really strong, but it looks like he's turned the corner. This time last year he was still two weeks away from going in for surgery, but this year we've had the time we needed between his surgery and the start of the season, so we should do better."

Taylor Garner
"He had an ankle reconstruction before last pre-season, so he's really not been able to get a lot of continuity in his work. But he's getting some really good volumes done now."

Robbie Tarrant
"He's done a really high volume of training for the last eight to 10 weeks and we've been able to transition him back into game sense over the last two and a half weeks."

Aaron Black
"It's been great to see him out there, he's been moving really well and looking confident. He's doing a full load of training, but we're still controlling some of the contact work. We will do that for another couple of weeks."

Majak Daw
"It's a really rare injury to dislocate your hind foot like Majak did, but he hasn't missed a beat this pre-season. He's doing really well."

Nathan Grima
"At the end of last season, we were able to give his navicular the rest that it really needed. He's actually way ahead of where he was this time last year in terms of the amount of work he's getting in."