ROBBIE Tarrant and Joel Tippett aren’t necessarily locked in a race to replace injured key defender Nathan Grima in round one, with North Melbourne coach Brad Scott saying there could be room for both talls in the Roos' backline.

Grima and Scott Thompson have held down North's key defensive posts in recent seasons, but the club will be without for Grima for the next three months as he recovers from back surgery last week.

North had already intended to switch Tarrant, 196cm and 96kg, from attack to defence before Grima's injury as the Roos looked to introduce a 'gorilla' to their backline in the wake of their inability to curb Tom Hawkins, Lance Franklin and Kurt Tippett (Joel's elder brother) in last year's finals series.

Like Tarrant, Joel Tippett, 197cm, missed North's 2014 finals campaign, but had shown promising signs in four senior games earlier last year before rupturing a pectoral muscle against Geelong in round 10.

Both Tarrant and Tippett should get their chance to press for a round one spot on Sunday after being selected in North's squad for its opening NAB Challenge clash against Adelaide in Port Lincoln.

Thompson will be missing from that side as he is eased back into match practice following pre-season knee surgery.

However, Scott told reporters on Thursday that Tarrant and Tippett could play in the same side alongside Thompson once the premiership season kicks off.

"They're both terrific athletes. Robbie in particular has been noted throughout his career as being just a tremendous athlete for someone his size," Scott said.

"So we think if players are mobile enough and quick enough then height's not really a factor for us. While we might look tall, as long as we're athletic enough that's OK.

"If they play well, they'll hold their spots."

Scott said North's growing depth meant there would be healthy competition for senior spots ahead of round one, making it unlikely that the Roos would be able to settle on their best 22 before then.

"We'll flick a lot of players through different positions and certainly toy with our defence a little bit," he said of North's NAB Challenge plans. 

"We've got the flexibility to structure up our forward line a bit differently so we'll have a look at all different aspects and probably play a few guys through the midfield who haven't spent much time in there before."

Sunday's clash with the Crows is a preview of the teams' round one fixture at Adelaide Oval on April 5.

Asked whether North would keep some tactical tricks up its sleeve this Sunday to keep the Crows guessing, Scott said he wasn’t about to flirt with form.

"We've trained all pre-season to practise some things so we're not going to try and hide those away just because we play the Crows again in a month," he said.

"We've got to focus a bit on our own game. We can't be too cagey on that sort of stuff. We'll be trying to implement what we've been practising." 

North listed Lachie Hansen (hips) as being four weeks away from playing on Tuesday, but Scott was confident the key defender would be available for round one.

"He's feeling a lot better than the medical guys think he's going at the moment. He really feels like he could get into full training now," Scott said.

"He's actually doing quite a bit of work so I suspect once he comes back into full training he'll come to hand pretty quickly and be available for selection pretty quickly."

Robbie Tarrant is a $142,00 forward in NAB AFL Fantasy this year. Create and fill your AFL Fantasy Classic league by March 2 to win a free AFL Live pass.