Amir Khan defiantly insisted he was okay while he was taken to hospital as a precaution after his heavy sixth-round knockout defeat by Saul "Canelo" Alvarez in Las Vegas.
The WBC champion brutally stopped Khan with a huge right hand to make the first successful defence of his title, inflicting the fourth loss of the 29-year-old's professional career and exposing him as a natural welterweight too small to convincingly compete at the catchweight of 155lbs.
There was little shame in the nature of the defeat for Khan, who impressed with his speed and combinations in the opening five rounds until Alvarez's superior size and strength began to slow him down and leave him vulnerable to the knockout that followed.
He said afterwards he expects to return to 147lbs, where he is undefeated and where his domestic rival Kell Brook is the IBF champion.
The Briton hit the canvas so heavily it was instantly obvious the fight was over - the official time was two minutes and 37 seconds of the sixth round.
Khan told host HBO after he eventually got up: "I'm a natural 147 (pounds) fighter but this challenge came and it was very hard to turn down.
"I want to be the best, I want to fight the best and that's why I took this fight. I showed my bravery by getting in the ring with Canelo, but this is boxing.
"I wanted to go out there as a champion. I was unfortunate that I didn't make it to the end, but I tried my best and I want to say thank you for the support."
Harshly for Khan, by some distance the smaller fighter in the ring, only one of the three judges had him leading. Adailaide Byrd scored him 48-47 ahead at the point of the stoppage, while Glenn Trowbridge and Glenn Feldman surprisingly had Alvarez respectively leading 49-46 and 48-47.
Alvarez, who knelt beside Khan to check he was okay after delivering the knockout blow, stressed he was prepared to next fight the fearsome WBA and IBF champion Gennady Golovkin - who was present at the T-Mobile Arena - in a unification title fight.
The 25-year-old Mexican said: "It was a human reaction to (kneel down and) make sure he was okay and I'm glad he appears to be. You want to win by knockout but you don't want to hurt anybody."