London Irish back Theo Brophy Clews has announced his retirement from professional rugby at the age of 24 due to concussion.
The England Under-20 international, a fly-half or centre, said he would be putting his "short-term and long-term health at risk" if he continued playing.
Brophy Clews made his Irish debut during the 2015-16 season and was an important member of the Gallagher Premiership club's first-team squad.
His last appearance for the Exiles was against European Challenge Cup quarter-final opponents Bath six weeks ago, when he went off after just two minutes.
In an open letter to London Irish supporters, Brophy Clews said: "It is with a heavy heart that I write to announce my retirement from professional rugby due to concussion.
"After receiving advice from the medical staff at London Irish and the Complex Concussion Clinic, it's clear to me that I cannot continue to play, as I would be putting both my short-term and my long-term health at risk.
"There is obviously a lot of emotion involved in a decision like this.
"First and foremost, I recognise that my health is the most important thing to consider. I have to accept that I can no longer put my body and my head through the physical challenges required to be a top-level player.
"Secondly, I am hugely grateful for the time I've had in the game, the people I've shared the pitch with, and being involved in the special community we have in English rugby.
"Lastly, I am incredibly sad. While I appreciate that there is so much more to live for and more important issues in the world, I am really going to miss it.
"The emotions you go through, the bonds and special memories you make with the people around you, let alone playing the game you love for a living, will all be incredibly tough to leave behind."
