Lambasted by ex-Sydney coach Paul Roos for not being fit enough to play in the midfield, North Melbourne youngster Jack Ziebell took the criticism on the chin.

It didn't knock him to the canvas.

It sent him to the gym.

A gruelling training regimen since has the 20-year-old playing some of the best football of his AFL career, given him the ability to match tanks with most in the midfield, and importantly helped the Kangaroos to two successive wins to clamber into finals contention.

Commentating for television during North's loss to Richmond in April, the respected Roos said Ziebell was lacking the fitness to successfully play midfield in the AFL.

Roos suggested Ziebell be dropped to the reserves.

Kangaroos coach Brad Scott decided otherwise, keeping Ziebell in the seniors to work harder and giving him an extra training workload.

"It was fair criticism. I wasn't up to the standard I needed to be at," Ziebell told AAP.

"I was playing low on confidence too as well which is pretty hard to do.

"But I appreciated the coaches sticking by me, chucking me in there (the midfield). I think that's where they see me playing and that's where I want to be playing as well.

"Brad backed me in. It's been a good turnaround."

Ziebell was among North's best in a big win over Gold Coast last weekend, and also impressed in the Kangaroos' victory over Melbourne last month.

Far behind him are the injuries which caused his fitness issues.

Interrupted pre-seasons and two broken legs which cut previous seasons in half have allowed him to get a consistent sequence of games under his belt.

"It was a slow start to the year and I've missed a lot of footy over the last couple of years, and I don't think that helped," he said.

"But it took me a couple of games to get into it, especially the match fitness.

"I sat down with the coaches and started doing a fair few extras (training), and that's starting to kick in now.

"It's given me a lot of confidence."

Having climbed to within sight of the top eight, the Kangaroos face a massive test on Saturday against fellow finals aspirants Essendon at Etihad Stadium.

For North, it's a chance to springboard towards a better second half of the season and beat another young, developing team.

"We've got two in a row for the first time this year and there's a bit of a buoyant feeling around the club," Ziebell said.

"Essendon are a good side, but hopefully we can win this and we've got a couple of other winnable games coming up."

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