The troublesome nature of Jarrad Waite's hip injury means North Melbourne cannot be sure of the forward's ability to stay fit.

Waite kicked two goals in his side's 23-point win against St Kilda on Saturday night at Etihad Stadium, to help his side all but seal a spot in the finals.

Whether the 33-year-old can consistently contribute for the rest of the season is in doubt though after he sat out much of the second half because of a jarred hip.

The Roo went into the rooms at the quarter-time break, received treatment while on the bench towards the end of the second quarter and did not return to the field after booting his second goal minutes into the third term.

He looked sore and hampered by the same concern that caused him to miss five of the six games leading into the clash versus the Saints.

North Melbourne coach Brad Scott said after the game Waite had hurt himself in an innocuous manner.

"I understand he's been in the side, then out, then in, then out, in quick succession. For our supporters and members, he looks like he's just jarred his hip again, the same hip," Scott said.

"Whether it's exactly the same injury, I'm not sure.

"It's a strange one, because you saw how he was functioning right at the start of the game, and then five minutes later, without incident, he's pretty sore."

Waite will have the scans before the club decides how to treat him.

"I'm not acutely concerned, because it's been an ongoing thing for probably six weeks," Scott said.

"The biggest challenge is he feels perfect one minute and sore the next. It's really hard for the medical staff to give a definitive diagnosis, but we'll go back to the drawing board and hopefully get him back next week.

"Clearly, we brought him back (for) two games, and he hasn’t got through those two games."

While the Roos are all but assured their place in the finals after the win, where they ultimately finish will rest on their record in the final four weeks of the home and away season, with matches against fellow top-eight opponents: the Western Bulldogs, Hawthorn, the Sydney Swans and Greater Western Sydney.

Drew Petrie starred against the Saints with 18 disposals, 12 marks and two goals in a performance that erased any doubts about his form.

However, for Scott, there had never been any questions over the 33-year-old's standard of play.

"There were never any questions internally. We've said that. Whether people believe you or not, it's up to them," Scott said.

"We understand we live in an opinion-based industry, and people have got every right to express their opinion, but I just as coach try and focus on the facts.

"Particularly players of the calibre of Drew Petrie, you just know that if you continue to support them and work with them, it's only a matter of time."

Brent Harvey continued his perfect record in milestone games, with his 427th match breaking Michael Tuck's mark for most matches played. Scott said it was doubtful anyone would ever line up on more occasions than the 38-year-old Harvey.

"I can't see this record being equalled or broken in my lifetime. The game is more arduous than ever, and I think the thing that impresses me the most is he's not just limping to the line," Scott said.

"He's broken the all-time games record, arguably at the peak of his powers, which is something to behold."

The Roos face the Dogs next Saturday night at Etihad Stadium.