NORTH Melbourne midfielder Daniel Wells is in doubt for round one despite a gruelling fitness campaign following his return from life-threatening blood clots.

The reigning Syd Barker medallist suffered complications after shoulder surgery in September, with doctors discovering blood clots on both lungs.

Wells must avoid all contact until cleared to return, but the Herald Sun reports the 26-year-old has focused on building his upper body strength and aerobic capacity.

"He has been progressing really well. He has done all the fitness and conditioning work - all the running - and he's back into leg weights and core work,"  North Melbourne medical services director Steve Saunders said.

"His shoulder and upper body work is still modified because of [the] surgery, but until he's off the blood thinners we won't run the risk of any contact at all.

"There is a hell of a lot of footy work and training he can do."

Wells will remain on blood thinning medication until the end of March, the same time the Kangaroos kick off their season, meaning Wells may have to wait until round three or four to return.

"It's the end of March [until he's off the blood-thinners], so we will keep him away from that [contact] stuff until then," Saunders said.

"We will see where he's at then and try as best we can to ascertain how many weeks of contact work he will need until he's ready to play.

"He is the sort of player who won't need too much in terms of that final bit of preparation."