Geelong midfielder Sam Blease has become the third player forced into retirement because of concussion this year.
In a strong sign clubs and players are improving their handling of head injuries, Blease, a former Demon, joins North Melbourne's Leigh Adams and Brisbane's Matt Maguire in retirement.
He has not played since he suffered a head knock in the VFL against Essendon on July 25 and has since been advised by specialists to avoid contact sports.
Blease, 24, managed just the one game for the Cats in his only season at the club. He had played in 33 matches for Melbourne, having been pick No.17 in the 2008 national draft.
Blease took to social media to thank the Demons and Cats for his opportunities but said it was "a shame it's ended due to concussion". He is set to return to his junior club, Norwood, in the Eastern Football League in an off-field role.
He had joined the Cats as a delisted free agent at the end of last season, having managed only two matches under Paul Roos last year.
Geelong football manager Steve Hocking said Blease had worked hard to rebuild his career.
"Sam was unfortunate this year as he was only able to be selected for 12 games in total across both our teams due to a variety of injuries," Hocking said.
The manner in which clubs and players handle head injuries has improved significantly in recent seasons, and comes at a time when the long-term impact of major knocks has prompted former players in the American National Football League to take legal action.
Scans had revealed Maguire had blood spots on his brain, and he experienced blurred vision and dizziness when trying to train with intensity after he was knocked unconscious in a reserves game.
Adams endured three head knocks last season and was ruled out of the Kangaroos' finals campaign. He was then concussed in a VFL practice match this year, prompting him to weigh up his future.
"One in two people with concussion get depression," he said. "And I got it pretty bad there for probably three or four weeks where it didn't matter what was happening."
"I just thought the world was against me. I'd had enough and was just sick of getting knocked around."
Brisbane great Jonathan Brown retired last year after a series of head knocks.
As revealed in June, The AFL Players Association has contacted all players who have suffered a concussion this season in order to make sure they have been treated "seriously".
Concussion campaigner and player agent Peter Jess has maintained his call for greater match-day testing.
More than 2500 former VFL-AFL players were also given a questionnaire last year asking for feedback on the impact of head knocks.
