Ten former rugby league players, including ex-Great Britain scrum-half Bobbie Goulding, are claiming the sport has left them with brain damage.
Lawyers say the players are all suffering from “neurological complications”.
And they are now planning a legal claim against the Rugby Football League for negligence.
It follows similar action by rugby union players including England’s World Cup winner Steve Thompson.
Goulding, who has recently been diagnosed with early-onset dementia, said there was not enough protection for players who had suffered head injuries.
The 49-year-old, who won the Super League and Challenge Cup double in 1996 as St Helens captain, said he had played again within days of being knocked unconscious at least three times in his career.
Former Wales international Michael Edwards, 48, and Scotland internationals Jason Roach, 50, and Ryan MacDonald, 43, are also part of a test group of 10 players, all under the age of 60, bringing the legal action. All three have also been diagnosed with early-onset dementia.
Their lawyer, Richard Boardman, said he was representing a total of 50 former professional rugby league players in their 20s to 50s, all of whom are showing symptoms associated with neurological complications.
He is also representing 175 former rugby union players, including Thompson, in a separate lawsuit.
Boardman said the legal claim was not just about financial compensation, but making the game safer and getting tested and diagnosed to undertake urgent clinical support.
He said there were potentially hundreds of former rugby league players who, as they reached their 40s and 50s, were developing various neurological issues, such as early-onset dementia, CTE (chronic traumatic encephalopathy), epilepsy, Parkinson’s disease and motor neurone disease.
“The vast majority of the former players we represent love the game and don’t want to see it harmed in any way,” Boardman said.
“They just want to make it safer so current and future generations don’t end up like them. We’re asking the RFL to make a number of immediate, relatively low-cost changes to save the sport, such as limiting contact in training and extending the return to play following a concussion.”
Given the significant risk of serious or permanent brain damage caused by concussions, the former players allege the RFL owed them – as individual professional players – a duty to take reasonable care for their safety.
Boardman added the group also felt the RFL should have established and implemented rules on the assessment, diagnosis and treatment of actual or suspected concussive injuries.
In a statement the RFL said: “The Rugby Football League has recently been contacted by solicitors representing a number of former players.
“The RFL takes player safety and welfare extremely seriously and has been saddened to hear about some of the former players’ difficulties.
“Rugby league is a contact sport and, while there is an element of risk to playing any sport, player welfare is always of paramount importance.
“As a result of scientific knowledge, the sport of rugby league continues to improve and develop its approach to concussion, head injury assessment, education, management and prevention across the whole game. We will continue to use medical evidence and research to reinforce and enhance our approach.”
‘I didn’t have one doctor check on me after knockout’
Goulding played for sides including Wigan, Leeds, Widnes and St Helens as well as earning 17 caps for Great Britain. He played for England five times, including the World Cup final in 1995, and the following year was named in the Super League team of the season.
Since retiring, first in 2005 and then nine years later after a brief comeback with Barrow Raiders, he has spoken about his battles with alcohol and drug addiction.
Talking about his dementia diagnosis, Goulding said: “For something like this to come out of the blue, and hit me like a bus, is hard to take.
“I didn’t think about dementia at all, I just thought it was the way life was.
“I played within days of serious knockouts on at least three occasions. I remember playing on a Sunday for Leigh at Huddersfield towards the end of my career [in 2002].
“I was in Huddersfield Royal Infirmary on the Sunday night after being seriously knocked out and played the following Saturday against Batley. I didn’t have one doctor check on me during that week.”
What is CTE & how can it be diagnosed?
Many of the former rugby league players who form part of the legal case have been diagnosed with early-onset dementia and probable CTE.
CTE is the disease discovered by Dr Bennet Omalu in American football player Mike Webster, and the subject of the film Concussion starring Will Smith. In 2011, a group of former American footballers started a class action against the NFL and won a settlement worth about $1bn (£700m).
CTE can develop when the brain is subjected to numerous small blows or rapid movements – sometimes known as sub-concussions – and is associated with symptoms such as memory loss, depression and progressive dementia.
The disease can only be diagnosed in a brain after death.
It has been found in the brains of dozens of former NFL players, as well as a handful of deceased footballers, including former West Bromwich Albion and England striker Jeff Astle. A re-examination of his brain in 2014 found he had died from CTE.
The issue of concussion in sport has been debated extensively over the past few years and the links between heading a football and degenerative brain disease have even forced rule changes at youth level.
In England, Scotland and Northern Ireland, children aged 11 and under are no longer allowed to head a ball in training, while there are also limits to heading frequency at higher age group levels.
At senior level, former professionals have called for more research and better player welfare after the death of England World Cup winner Nobby Stiles a year ago, and news that his 1966 team-mate and Manchester United legend Sir Bobby Charlton is also suffering from the disease.
More information about dementia and details of organisations that can help can be found here.