Britain's Olympic silver medallist Michael Jamieson may retire after failing to qualify for Rio 2016.
The Scot, 28, came fifth in the 200m breaststroke final at the British trials in Glasgow on Friday, with only the top two considered for selection.
Jamieson has endured a difficult two years, including suffering a heart scare and losing to rival Ross Murdoch in his home Commonwealth Games.
"My body just can't take the intensity any more," Jamieson told BBC Sport.
Andrew Willis was the surprise winner of the 200m in Glasgow, with Craig Benson second and Commonwealth champion and pre-race favourite Ross Murdoch third.
Jamieson added: "Over the last couple of years there have been psychological challenges because I've been struggling for confidence, but I know my body well enough to know when it's responding and when it's not.
"I love to push myself to the limit and I'm not able to do that any more."
Jamieson was the highest-placed British swimmer at an otherwise disappointing London 2012.
He became the face of the sport and was named as an ambassador for the 2014 Commonwealth Games in Glasgow, the city of his birth.
Jamieson admitted he became "obsessed" with the pursuit of perfection and his intense work ethic led to an irregular heartbeat which required a defibrillator to resolve.
He also suffered with a chronic back problem in the build-up to the Glasgow Games and considered quitting the sport after losing to Murdoch.
Jamieson returned to the sport in late 2014, but missed out on selection for GB's record-breaking 2015 World Championships.
"I'm absolutely gutted, but that's two full years now that I've been quite a long way off my best," he said.
Jamieson finished in two minutes 10.55 seconds on Friday, almost two seconds outside the qualifying mark of 2:08.52.
"I've achieved the qualifying time seven or eight times in my career, but perhaps being so far away from that now makes it almost easier to accept," he said.
Jamieson, who will take time to decide on his next move, added: "London was such a special event and if I could go back and do it again then I'd love to.
"I wanted it to be the catapult so I could go on and dominate that event, but if I'd chilled out a bit more and reflected on that then perhaps the last few seasons may have gone differently.
"The standard in Britain is so high right now and whoever represents us in the breaststroke events in Rio will have a fantastic chance of a medal."
World champion Adam Peaty and Commonwealth bronze medallist Willis have secured Rio breaststroke places, while Murdoch and Benson remain in contention to make the GB squad.