Former Leeds Rhinos captain Stevie Ward has announced his retirement at the age of 27 because of the long-term effects of concussion.
Ward said he is unable to even exercise without "irritating his symptoms".
He missed the rest of the 2020 season after suffering a concussion in the Rhinos' opening game of the year.
The club stood him down "indefinitely" in February, with head coach Richard Agar saying at the time it was "concerning".
The loose forward's contract with Leeds, who were the only team he played for in his career, expired at the end of 2020.
He made 109 Super League appearances and won two Grand Finals and one Challenge Cup.
Ward said in a statement: "I have come to the conclusion, after over 11 months of severe symptoms, that I need to give this injury the respect and time it deserves and cannot put my health and brain to any further risk and detriment.
"On a daily basis, I struggle with migraines, dizziness, motion sickness, sensitivity to light and screens, short-term memory issues, slurred speech, and an inability to exercise or do daily tasks without irritating my symptoms.
"I love the game of rugby league. I am immensely proud to have competed on some of the biggest stages next to childhood heroes and test myself to the absolute limit while feeling the incredible buzz from the Leeds fans after being one myself as a youngster."
Ward revealed that he initially suffered a concussion in the pre-season friendly with Wigan last January before suffering a second against Hull FC in the Super League season-opener a fortnight later.
Ward wants changes implemented now
His retirement comes at a time when both codes of rugby and football are facing increased scrutiny about the long-term effects of concussion.
In December 2019, Ward's former Rhinos team-mate Rob Burrow was diagnosed with motor neurone disease and research has found former professional footballers were four times more likely to die of MND than the general population.
Last month Rugby World Cup winner Steve Thompson and seven other former union players claimed the sport has left them with permanent brain damage - and are in the process of starting a claim against the game's authorities for negligence.
Ward added that it was "laziness" to simply say "more research is needed" and it was time to be proactive about the "culture and stigma" around concussion.
"One of the biggest lessons I have learnt from last year is that enormous consideration needs to be taken when mixing the brutality of the game with the brain's fragility," he said.
"With the news about Rob and the current climate of rugby union players, I cannot help but ask the questions that need to be asked.
"I am left motivated to help get our sport to a place where it can ensure the players' long-term safety whilst keeping the beauty and grit of the game.
"Of course, more research is needed. However, I believe that there is an element of laziness with just making this statement."
He added: "It is now time to be asking and answering more specific questions. What will this research be? How will it be funded? How long will this new research take? And how do we focus our efforts in the meantime?
"The biggest question is what can be done to make things safer for our players now. We need to be more proactive and not rely on another generation of players to be guinea pigs for future research that will take years to give us the answers we need now."
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