North Melbourne coach Brad Scott says naming Brent Harvey as the substitute in the Kangaroos' win over Geelong was a warning to the veteran midfielder.

In a move that shocked many, Harvey, in his 398th game, was handed the green vest following what Scott described as a "pretty honest and frank conversation".

Before Saturday night, the 37-year-old had never started as a sub, nor been subbed out of a game.

Harvey struggled to fire in the Kangaroos' deplorable loss against Gold Coast last Saturday, despite tallying 23 disposals.

Scott said the green vest served as a warning to Harvey to heed the coach's instructions on game day.

"Boomer probably by his own admission hasn't performed the role we've asked him to play on a few occasions this year," Scott said after the 41-point win over the Cats.

"We had a pretty honest and frank conversation. We've got a great relationship and we talk all the time and it was a pretty simple coach-player conversation.

"Whilst being the sub wasn't a punishment, he needed to know that if he's not going to listen to my words, he might listen to my actions."

PRESS PLAY above to watch the Scott media conference | YouTube

Harvey is on track to play his 400th game in round 17 against the Brisbane Lions at the Gabba.

Questions surrounding his future beyond this season have been raised with Scott admitting the pair discuss the topic nearly every week.

Harvey maintains he will play on if his body can physically cope with the rigors of a 21st AFL season but Scott said the Roos midfielder would have to prove himself to the club before they extended his contract.

"The evidence will be really clear to Boomer and it'll be clear to the club whether the best decision is for him to go on," Scott said.

"As he's said a number of times, physically he feels great and if he can play the way we want him to play, there's no reason he can't go on. But I'm all about evidence, and if he provides the evidence then he should go on."

Itching to get off the bench on Saturday night against the Cats, Harvey came on in the final term after youngster Kayne Turner was subbed out of the game with concussion, and had an immediate impact.

The veteran looked dangerous at times, missing a shot at goal but managed to collect 14 disposals and had four inside 50s and a score assist.

Scott said Harvey had handled being the substitute with aplomb but didn't rule out using him in the same role again in the future.

"It is a role that we've spoken about over the last couple of years," he said.

"We think it can be a real weapon for us going forward. It probably just took the courage to pull the trigger and do it, because it was a big game for us against a really strong opposition club.

"Brent was outstanding from yesterday's meeting, right through to the end of the game today in terms of how he embraced that role."

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