MELBOURNE'S unbeaten start to the season has hit a major stumbling block with fears that in-form defender Adam Tomlinson has ruptured his anterior cruciate ligament. 

Tomlinson hurt his left knee during an innocuous contest in the first quarter of the Demons' 30-point victory over the Kangaroos on Sunday.

KANGAROOS v DEMONS Full match coverage and stats

While the club awaits scans to confirm the severity of the injury, coach Simon Goodwin said the initial diagnosis was that Tomlinson had suffered an ACL injury that will leave him sidelined for the remainder of the season.

"He's shattered," Goodwin told reporters after the match.

"He has put in a lot of work to get his game to the position it is and for coaches and players we have got incredible care and connection for each other at the moment and Adam has been a big part of that.

"It is looking like an ACL, but we will get scans to confirm that. It is really disappointing for him."

Tomlinson has been one of the club's most consistent performers in 2021 and Goodwin knows his absence will be difficult to cover.

"It (defence) is one of those areas we have been real strong in and he has done an incredible job in helping us and enabling us to do the things with (Steven) May and (Jake) Lever," Goodwin said.

"We have got a couple of options that we will look at as a coaching group, but we will have to restructure a little bit behind the footy."

With Tomlinson watching on as a forlorn figure on the bench, swingman Tom McDonald was moved to defence for the second half against the Roos and played a pivotal part in the turnaround that helped the Dees remain unbeaten this season.

Whether or not McDonald continues in that defensive role remains to be seen, although Goodwin does have a number of forward options as his disposal with former Kangaroo Ben Brown slotting into the line-up on Sunday and youngster Sam Weideman still biding his time in the VFL.

Brown booted two goals for the Demons in his first senior game at his new club, while Weideman has kicked 14 goals through three games at the lower level already this year.

Goodwin also singled out youngster Harrison Petty as another option as a direct replacement for Tomlinson should he want to continue with McDonald alongside Brown in attack.

"Harrison Petty played a few weeks ago and is ready to play some good AFL footy so that is exciting for us that he will get an opportunity and Tom McDonald, as you saw today, we pushed him back and he performed really strongly," Goodwin said.

"Competition for spots is healthy and we will keep picking the team that we think is best for the opposition and the way we want to play."

There were mixed emotions for North Melbourne coach David Noble, who remains steadfast in his belief that his young team is working closer to its first win of the season.

"That (first half) was certainly our best half (of the season) by far," Noble said.

"I know we didn't necessarily get the job done in the third quarter, but I also look at the fact that we kicked the first goal of the last quarter and were right in the game.

"The way we defended in that first half is certainly the blueprint we want to go forward with."

North Melbourne will get another crack at registering its first win of the season when it tackles fellow struggler Collingwood next round.

Noble is hopeful that Aiden Bonar will be fit, after the in-form defender was subbed out of the clash with the Demons due to a corked thigh.