NORTH Melbourne's Leigh Adams has been forced into retirement by a series of head knocks that have prevented him from playing a single AFL game this season.

Adams, who has only managed three VFL games in 2015, announced the decision to his teammates on Friday, calling time on a 104-game career.  

The 27-year-old revealed his battle with short-term depression earlier this year when a head knock in March almost led him to quit. 

He was able to return to the VFL in round nine, but in his third game back the hard-nosed forward suffered another head knock that has sidelined him since. 

Adams made his name as a courageous player who would burrow in at stoppages and puts his body on the line. It was a style that led to several concussions over his nine years in the AFL.

Coach Brad Scott said Adams, who was known affectionately as 'Patch', had shown great commitment to his teammates and redefined the forward/midfielder role.

"'Patch' was such a highly valued person and highly valued performer for us over such a long period," Scott said.

"But we know there are things that are more important than the game.

"As a footy club, I’m proud of the way everyone has supported 'Patch' through a really difficult time and certainly support his decision."

Adams suffered three separate head knocks last year, in rounds 12, 18 and 23, ruling him out of the Kangaroos' finals campaign.

His first concussion this year occurred in a practice match between North Melbourne's VFL affiliate Werribee and Footscray.

That injury left Adams contemplating his future and dealing with a mental struggle.

"One in two people with concussion get depression … and I got it pretty bad there for probably three or four weeks where it didn’t matter what was happening," Adams said in June.

"I just thought the world was against me and ‘poor me’ and ‘nah, I don’t want to play anymore’.

"I’d had enough and was just sick of getting knocked around." 

Not long after speaking publicly about that concussion, Adams suffered his latest head knock in the VFL, which has ultimately ended his career. 

The popular Kangaroo was recruited with pick No.3 in the 2006 Rookie Draft.