JUST two months ago, Geelong forward Cameron Mooney admitted his chronic knee problem might cause him to retire before the season is over.

But how the thought of running onto the MCG to take on Collingwood, before an expected Friday-night crowd of more than 80,000, can soothe a veteran footballer's aching joints.

Speaking two days after the Cats' clinical 66-point win over North Melbourne at Skilled Stadium in round seven, Mooney was as upbeat as he's been all year.

"I feel really good actually," the 31-year-old said. "My back's a little bit stiff but I just put that down to old age these days."

Mooney, whose "general soreness" kept him out of Geelong's win over Hawthorn in round six, started up forward in the easy victory over the Kangaroos.

He later spent some time in the ruck after Brad Ottens was subbed out of the game at half time so he could rest up for the clash with the Magpies.

"I really enjoyed that, to be honest," the three-time premiership player said. "I've missed a fair bit of pre-season, so I'm a long way behind all the other boys.

"I'm gradually just getting my fitness back up, so I needed a run on the ball to try and get some run in my legs.

"It was great fun in the end."

Against Collingwood, Mooney is again likely to spend some time in the ruck as the Cats try to subdue to the influence of Cameron Wood and Leigh Brown (the Magpies' number one big man, Darren Jolly, has already been ruled out with a knee injury).

While Geelong has a number of back-up ruckmen - Mark Blake, Dawson Simpson, Nathan Vardy and Trent West - in its reserves team, Mooney believes it is unlikely the Cats will select one of them if Ottens is fit.

"As far as having another ruckman in the side, those days are over unless you've got great ruckmen like Essendon have," Mooney said, pointing the Bombers' decision to play David Hille, Patrick Ryder and Tom Bellchambers in some games this season.

"Myself and 'Hawk' [Tom Hawkins], we'll definitely keep rotating through their during the year to give Otto a chop-out."

Geelong has defied its doubters to be undefeated after seven rounds.

"I'm not surprised, but we've been very fortunate to be honest," Mooney said.

"We had two games against St Kilda and Fremantle [in rounds one and two] where we could have lost quite easily.

"It's a funny thing, footy. We could've been zip and two, instead we were two and zip.

"Then we've got on a roll and have been going well."

Like most of his teammates, Mooney has played in a host of blockbuster matches during the Cats' recent period of success.

But he never tires of getting the opportunity to take on big clubs like Collingwood.

"I guess this is one of those games you really don't want to miss," he said of Friday night's much-anticipated contest.

"It's something I'm very proud of that, after five years [at the top], the boys are still up and about.

"Most teams fall away after a couple of years, but we've got that hunger and passion to really keep fighting and that's what keeps us going."

Adam McNicol covers Geelong news for afl.com.au. Follow him on Twitter: @AFL_AdamMcNicol