Collingwood star Darcy Moore shook off an illness concern just hours out from the Magpies' semi-final win over Fremantle to help lead his side to victory, with the key defender bed-ridden in the days leading up to the match.

A matchday phone call to Craig McRae from the doctor was enough to worry the Magpies senior coach on Saturday morning before any remaining concerns were cleared when Moore was deemed fit to feature in the eventual 20-point win.

The All-Australian backman showed no signs of an illness impacting his ability against the Dockers, with Moore among the Magpies' best for the night as they secured themselves a preliminary finals berth.

Speaking after the match, McRae revealed Moore had been battling a bug, stating there was "some concern" his backman could've missed the clash.

"He's been sick all week," McRae said.

"I thought he was pretty good tonight. I think if you look back at how he played and intercept. The guy's been in bed for a couple of days ill.

"...I hate it when the doctor rings me matchday. There was some concern. Confidence was still there but there was some concern."

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Moore flexed his ability to close down aerial contests, lock down his direct opponent and hinder any avenues the Dockers had opened toward goal.

The 26-year-old's performance was one that rivalled his stellar efforts the week prior against Geelong where he also led from the last line.

Teammate Isaac Quaynor revelled in being able to rely on his fellow backman throughout the match.

"He's one of those players that when you're side by side with him you walk a bit taller," Quaynor told Zero Hanger. 

"That close-down speed, not many players in this competition can do that.

"He's just a really special player and I love going out there and playing with him."

Saturday night's wins see Collinwood progress to the penultimate Saturday of the season, with the Magpies to face Sydney at the SCG on September 17 in hope of booking their place in the grand final.