FORMER Australia captain Boyd Cordner has announced his retirement at the age of 29 after a succession of concussions.

The Sydney Roosters and New South Wales skipper, who has not played this season due to a history of head knocks, says he made the announcement on medical advice.

Cordner, who played 181 games for the Roosters, 16 in State of Origin and 20 for the Kangaroos, fought back the tears at a press conference on Monday as he confirmed the "toughest decision I've ever made".

"I'm proud that I've come to this decision," Cordner said. "The easiest thing for me would've been to say nothing and play on. But I know now that this is the toughest thing that I've had to do.

"Deep down I knew I wasn't 100 per cent fully recovered. I was at a stage where I was at full training with the guys and I was very close to 100 per cent but the feeling of going out and (thinking), 'what does the next head knock look like for me?'... I couldn't get that out of my head.

"If I ever did get another head knock I don't know if I could have lived with myself... I've played on with everything.

"It's pretty well documented (about) my body breaking down like a two-door car. I've been able to pick myself up and if I want to go, my body just goes. But I knew this was different because I couldn't get my head and heart to align."

The second rower scored the only try and was named man of the match in Australia's 6-0 win over England in the 2017 World Cup final in Brisbane.

Cordner is the second Roosters player to retire this season due to persistent concussions after hooker Jake Friend ended his career at the age of 31.