Former New Zealand prop Carl Hayman has revealed he has been diagnosed with early-onset dementia aged just 41.

Hayman, who earned 45 Test caps before playing for Newcastle Falcons and Toulon, sought medical advice after experiencing memory loss, confusion and suicidal thoughts.

"I spent several years thinking I was going crazy," he told The Bounce.

"It was the constant headaches and all these things going on that I couldn't understand."

Hayman said tests showed he had early-onset dementia and probable chronic traumatic encephalopathy (CTE) - a neurodegenerative disease.

The diagnosis prompted him to join a lawsuit brought by similarly affected ex-players, including England's Steve Thompson and Alix Popham of Wales, against the sport's governing bodies, including World Rugby.

The basis of the players' claim is that rugby authorities failed to provide sufficient protection when the risks of concussion and sub-concussive injuries were "known and foreseeable".

Hayman said one reason for joining the legal action was to force fundamental changes to the game to minimise the risk of head injuries.

"[I] hope that the players of the future don't fall into the same trap that I did, that they're not treated like an object and are looked after better," he said.

"These younger aspiring players need to know what they're getting into and there needs to be more support and better monitoring around head injuries and workloads."

New Zealand Rugby (NZR) chief executive Mark Robinson said his thoughts were with Hayman, who is his former Test team-mate.

Robinson said NZR is developing world-leading policies and research on concussion aimed at protecting players at all levels of the game.

World Rugby said it had not been contacted by Hayman and could not comment on specifics of the legal action adding "player welfare is the sport's top priority".