Sale Sharks are fighting legal action by former player Cillian Willis, who claims they mishandled the injury that forced him to retire at 28.

The former scrum-half was knocked out in an LV Cup game against Saracens in 2013 before being allowed to play on by Sale’s medical team.

He was later replaced but was told to never play again after suffering previous concussions.

Cillian Willis (left) was knocked out in an LV Cup game against Saracens back in 2013

Willis is believed to be the first to take legal action against an Aviva Premiership club for medical negligence and the case could set a precedent.

Last week, Connacht centre Dave McSharry, 26, retired on the advice of a neurologist. ‘It is the only decision available to me after speaking to the specialist,’ said McSharry, who had suffered several concussions in the past 18 months.

There is concern that insurance companies will refuse to pay players forced to retire as the result of more than one head injury.

Sale declined to comment when approached by the Mail on Sunday.