Scotland forward David Denton has been forced to retire from rugby on the advice of doctors.
The 29-year-old decided to hang up his boots after being told he would be risking his long-term health after an 11-month concussion battle.
Denton, who won the last of his 42 caps for Scotland in Argentina last summer, told The Times: “I have had this thing hanging over me for a long time now.
“Since the injury I have woken up every morning with pressure in my head and visual disturbances and not really knowing what is going on.
“Pretty much for that whole time I’ve been assuming that next week I will be better.
“Every time I tried to go through the comeback protocol, I’d fail. I’ve tried everything but nothing’s worked.”
Denton suffered a blow to the head during Leicester Tigers’ league game with Northampton Saints at Twickenham last October.
But his attempts to make a return to the game floundered before he was finally given the news by neurosurgeon Richard Sylvester he should call time on his career for his own good.
Had he been fit, Zimbabwe-born Denton would have been in contention for a place in Gregor Townsend’s Scotland squad for the World Cup in Japan.
And the No 8 – who qualified for Scots thanks to his Glaswegian mother – admits he will miss pulling on a dark blue jersey most.
“The idea of never being able to run out in front of 70,000 people at Murrayfield again is not enjoyable,” he said.
“I so want the boys to do well [in Japan] and would so want to be there but that is not going to happen.
“It is important to me that I don’t look back with sadness at what could have been, instead look forward and remain proud of what has been.
“There was a lot more I wanted to achieve. All of a sudden I am not able to do that.”
Denton’s international team-mate Ali Price admits rugby may never solve its concussion problem.
The scrum-half, who is in Japan preparing for Sunday’s World Cup opener against Ireland, said: “It’s always going to be an issue. It’s a contact sport and sadly these things are going to happen.
“It’s a shame for David and there are a few players who have had to call time on their careers with similar issues but you’re never going to stop it unless you declare the sport touch rugby from now on.
“There is always that risk that injuries like this will happen but World Rugby are leading the way in trying to minimise how often it happens.