The London High Court will hear a plea on Friday to combine claims from 475 former sportspeople suffering from neurological impairments into a group action lawsuit against the governing bodies of their sports, law firm Rylands Garth said.
The firm said on Tuesday it would seek a Group Litigation Order (GLO) for claims from 450 rugby players and 25 football players against global and British governing bodies in Rugby Union, Rugby League and football.
GLOs are commonly associated with industrial disease claims such as respiratory problems for coal miners.
A source at World Rugby told Reuters on Tuesday that the case involved 268 rugby union claimants.
The players allege the governing bodies failed in their duty of care, which exposed them to concussion and non-concussion injuries leading to disorders such as motor neurone disease, early onset dementia, chronic traumatic encephalopathy (CTE), epilepsy and Parkinson's disease.
"We are seeing the same worrying symptoms in numerous cases across all three contact sports," Rylands Garth said in a statement.
"These symptoms include chronic depression, aggression, significant memory loss, incontinence, drug and alcohol addiction and in some cases, suicide attempts."
World Rugby, England's Rugby Football Union (RFU) and the Welsh Rugby Union (WRU) said in a joint statement on Tuesday that they were saddened to hear about the struggles of former players.
"Despite court orders to do so, the players' lawyers have yet to provide full details of the claims being made against us and therefore we cannot comment on the ongoing legal action, nor reach out to the players directly," the governing bodies added.
"We would want players involved to know that we listen, we care and continue to champion player welfare as the sport's number one priority.
"Players and parents can have confidence that rugby is as safe as a contact sport can be. Rugby will always be led by the latest science when taking any action on player welfare."
Formal proceedings in the case were opened at the High Court in London on June 23.
World Rugby has taken several steps to mitigate the impact of concussion including introducing smart mouthguard technology for head impact assessment and starting trials to lower tackle height in community rugby.
"The whole of rugby cares deeply about all of our current and former players. We will never stand still when it comes to player welfare," the governing bodies added.