Leigh "Leroy" Brown is big but he's not bad. He proved that in 2010 when he became an AFL premiership player at Collingwood.

At the tender age of 29, Brown announced on Thursday that he would retire in October.

In the meantime, the former Fremantle and North Melbourne key forward has a finals campaign on his mind with the ladder-leading Magpies.

The 242-game veteran said his past three seasons at Collingwood had been really special.

"Hopefully, it can be even more special over the next five weeks," Brown said.

"To (coach) Mick (Malthouse) and to (football manager) Geoff Walsh for giving me that opportunity, after being de-listed from North Melbourne and when it all seemed gone, I'm very grateful and I'm forever in their debt."

Brown played six VFL games in 2010 before making a name for himself as the ultimate role player, holding down a key-forward post and playing as a vital back-up ruckman in a premiership side.

"Mick takes most of the credit for that one," Brown joked.

"There's two ruckmen running around. Geelong have got (Brad) Ottens and (Trent) West.

"That's just the way it fell last year and maybe it will fall again this year (a tandem role with Collingwood ruckman Darren Jolly in the finals series)."

Brown, who has coaching ambitions, said his decision to retire was "a bit of physical, a bit of mental".

Malthouse said he was staggered when Brown told him the news. He praised Brown's courage for retiring while still playing good football.

"But I've always preached if the glass is half full or has something left in it, it's a good time (to go)," Malthouse said.

Brown's 63 games for Fremantle (2000-02) and 118 matches for North Melbourne (2003-2008) produced few highlights that will stick in the minds of AFL fans.

But his deeds at Collingwood have made him a hero to the Black and White Army.

He said if people's perceptions of him had changed since he joined the Magpies, to elevate him from an also-ran to a champion role player, that was up to them.

But in his own eyes, he had always played the same way.

"I think from an outsider's perspective, maybe. From within, I feel like I've always played my role and helped out my team," the 1999 No.5 draft pick said.

Malthouse said he could recall watching Brown play in the VFL after being unable to get a senior game with North.

"I thought 'this bloke can still play league football'," Malthouse said.

Malthouse said Brown was a great bloke, a team man and a tough guy who rarely missed a game.

"He has been outstanding for us," Malthouse beamed.

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