Cardiff - Wales international forward Jonathan Thomas has called time on his career at the age of 32 because of epilepsy, his club Worcester announced on Tuesday.
Thomas was diagnosed with epilepsy last year "which is thought to be from multiple head traumas and has led to a degree of brain injury," the club said in a statement.
Thomas, who won 67 Wales caps between 2003 and 2011 and played in two World Cups, has now stepped down on medical advice.
He also featured in two Six Nations Grand Slam campaigns with Wales and spent 10 years with the Ospreys before moving to Worcester in 2013.
Worcester high performance director Nick Johnston said: "We've sought the best medical opinion in the country in order to try and enable Jonathan to prolong his career.
"But unfortunately, on the advice of consultants, he has been advised to retire from professional rugby."
News of his retirement comes as the World Cup prepares to kick off in England later this week, with the debate concerning head impacts and concussion dominating rugby union's agenda in recent months.