Collingwood's forwards have been put on notice by coach Nathan Buckley after a flat performance against North Melbourne that effectively eliminated the Magpies from the pack chasing September action. 

Finals are now a pipe dream after the form of the past month was undone with a six-goal-to-one start that left the Magpies on the back foot on Friday night.

Coach Nathan Buckley described his forward line as "impotent" in the first half and said the entire group was on notice after failing to win the ground ball and kicking 12.12 from 49 inside 50s.

"We keep shuffling it around and looking for who's going to be our next best side … but individuals had a chance to reinforce it and some did and some didn't," the coach said. 

"We were impotent forward of the ball for most of the first half, and we thought we went in with one of our better forward lines on paper for the year.

"Our forwards just didn't work hard enough to provide clear and legitimate options for the ball carrier.

"We just didn't have enough energy in the front half in that first half."

The Magpies sent defender Jeremy Howe forward in the second half and benefited, but it was too little too late, Buckley said. 

Asked for his thoughts on Travis Cloke's scoreless game, the coach simply said he was "part of a forward line that really struggled".

"I think all of the forwards are probably on notice at the moment," Buckley said. 

Friday night's game was billed a 'mini final', and the coach said that was how his team had approached the past month, resulting in a 4-1 run going into round 18.    

He was in no doubt the Kangaroos had taken a similar approach into the clash after a 0-5 run that saw them drop from first to eighth on the ladder.  

"This was the line in the sand … whatever you want to call it, this was it," the coach said.

"Whether they communicate that or not, I'm pretty sure internally they needed to get their season back on track.

"We knew all of that and it was going to be a tough ask. If we were able to get the job done tonight it would have been the performance of our season.

"We were up against a motivated and experienced team that just needed to get the job done, and in the end that's what they did."

Buckley welcomed looming matches against West Coast, the Western Bulldogs and Hawthorn as a chance to identify players who welcomed the big stage.

"We've had that opportunity the past two or three weeks and we've got it in the last part of the season as well," he said.

"We want to find out who can stand up and we want to give exposure to players who have actually put some pretty good form together and see how they handle this sort of pressure against really good footy sides.

"We're getting some pretty good feedback at the moment."