Biarritz veteran prop Eduard Coetzee announced he was retiring after being told by doctors that he had taken too many blows to the head.
The 32-year-old South African-born naturalised Frenchman - who has been at Biarritz since 2007 - said he had sought advice from several specialists before taking the decision.
"For me it is over as far as rugby is concerned," said Coetzee, whose contract was not due to expire until 2013.
"I consulted three different neurologists including two who work with the National Rugby League (LNR) and those last two and they formally forbade me to play rugby at the highest level."
Coetzee, who played for the Bulls and the Sharks in South Africa before joining Bayonne in 2005, said that he had especially suffered this season.
"I have already been knocked out three times since the beginning of the campaign," he said.
"Once against London Irish in a friendly, and then against Toulouse and Perpignan in the Top championship," added Coetzee, who also suffered a mild fit while training in between the Toulouse and Perpignan games.
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