London sports law firm Rylands Garth said it would issue proceedings in court on Tuesday on behalf of 100 rugby league players, 40 rugby union players and 15 football players, taking the total number of claimants to 380.
The players allege that the sports' governing bodies failed to protect them from concussion and non-concussion injuries that caused various disorders including early onset dementia, chronic traumatic encephalopathy, epilepsy, Parkinson's disease and motor neurone disease.
"Acting on the latest science, evidence and independent expert guidance, we constantly strive to safeguard and support all our players – future, current, and former...," World Rugby, the Rugby Football Union (RFU) and the Welsh Rugby Union (WRU) said in a joint statement.
Rylands Garth represents over 250 rugby union players with brain damage, including England World Cup winner Steve Thompson and former Wales captain Ryan Jones, in a claim against World Rugby and the governing bodies of England and Wales.
The firm also represents 100 rugby league players as part of a separate but similar potential claim against England's RFL.