Boxing manager Frank Maloney has been treated for a suspected heart attack after finding one of the sport's most promising young fighters hanged in his flat.
Olympic bronze medallist Darren Sutherland, 27, was found on Monday by his manager Maloney, 55, who was then taken to hospital for tests.
Sutherland's friend and one of Britain's top young boxers, Tony Jeffries, called the past 24 hours "a nightmare day".
The 24-year-old said: "Frank was really close to Darren. He was not just his promoter or his manager - he was a good friend. It was special and they were close.
"Frank's family were also close to Darren so I cannot imagine what it was like for Frank to find him.
"I am just so sorry. Frank is a great man and one of the best promoters. I just hope he recovers well and gets better soon."
Maloney's website has a front-page tribute to Sutherland, calling him "the Olympic bronze medallist with a golden heart".
Maloney was taken to hospital after finding Sutherland, nicknamed The Dazzler, at his flat in Bromley, south London.
Tests showed Maloney had recently suffered a heart attack.
Doctors at Bromley's Princess Royal University Hospital decided to keep him under observation, although he was well enough to sit up and work on his laptop, his spokesman said.
Irish fighter Sutherland won his four professional fights as a super-middleweight.
Tributes
Britain's James DeGale, who beat Sutherland in the Olympic semi-finals in 2008 before going on to win gold, described him as "an excellent fighter" and "a gentleman", while Dominic O'Rourke, president of the Irish Amateur Boxing Association, said the Dubliner had been "a star of the show" in Beijing.
O'Rourke said that Sutherland's death had devastated the fighters he grew up with in the domestic ranks.
"They're all in desperate shock," he said. "I'm totally shocked, it's unbelievable and it's a tragedy for all concerned.
"His family must be devastated, and our condolences go to them."
Irish boxing legend Barry McGuigan, the former world featherweight champion, believes Sutherland had the talent to go all the way to the top.
McGuigan said: "I am deeply shocked and deeply saddened by this news and my heart goes out to Darren's family. It is an absolute tragedy. I would describe Darren as a phenomenal talent.
"He represented his country with pride as an amateur and I believe he would have become a world champion in the professional ranks one day."
© Press Association