RYAN Nyhuis had never played in attack in his two seasons with Fremantle before his game-winning four-goal performance against North Melbourne at Etihad Stadium on Sunday.

Recruited from the NT Thunder at pick No.34 in the 2015 NAB AFL Rookie Draft, Nyhuis had played as a half-back and occasional run-with midfielder before getting a late call-up to replace David Mundy (illness) in Sunday's game.

Freo coach Ross Lyon said Nyhuis' debut was a really good story and a reminder that a player's desire to make the most of his opportunities is more important than his draft position.

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"Ryan took some half opportunities (against North), but he's invested so much in his footy, worked his way off the rookie list and that's probably the story we're talking about," Lyon said.

"No one wants to really talk about rookies but the reality is you need to bring rookies through. The commentary is caught up on where you got drafted and what draft pick you were and that's not the reality of AFL footy.

"The reality of AFL footy is you get an opportunity, you work hard and you grab your opportunities. I don't see a lot of first picks being showered down on us as a club, so we're going to have to work our way through that."

WATCH: Nyhuis' dream debut

Nyhuis found out on Saturday night he was a "70:30" chance to debut against North after former skipper Mundy became ill on the team flight to Melbourne.

The 20-year-old called his parents in the Northern Territory that night and they, as part of a group of 12 family members and friends, flew down just in case.

Nyhuis received confirmation he was playing at 10am on Sunday, with Lyon asking development coach Adam Read to break the good news given how closely the pair had worked together at Fremantle.

Lyon joked that Freo's coaching group must have been "asleep" not to have tried Nyhuis in attack before Sunday's game, but said the former rookie now faced the challenge of cementing a senior spot.

"I think he showed he can do it, but again league footy is not about one week. the challenge is over a period of time, enduring and surviving and flourishing in the end. He's got plenty of work to do," Lyon said.

"It's a really good story, but I've got a view that if you can play you can play anywhere. So if you can play in defence, you can play forward.

WATCH: Ross Lyon's full post-match media conference

"He can play, and when you're invested you'll take any little scrap you can get. But he's dog hungry so he fought today.

"I think we've got to recognise that side of it. It was really pleasing."

Fremantle's ability to fight back when North took the lead for the first time at the 18-minute mark of the final quarter was courageous given Tom Sheridan (hamstring) did not play in the second half and Joel Hamling (hip) had been noticeably restricted since midway through the first quarter.

Lyon said Sheridan's injury seemed to be a "standard" strain that would sideline him for 21 days, which would rule him out of the Dockers' upcoming clashes against West Coast, Hawthorn and, possibly, Greater Western Sydney.

The Freo coach was more optimistic about Hamling's injury.

"He had a bit of a hip that he tweaked. He just lost some power in it. He wasn't in any pain, but he just lost that power," Lyon said.