Nigel Doughty, the owner of second-tier English football team Nottingham Forest, was found dead at his home on Saturday.
The announcement by the former European champions, triggered tributes from ex-prime ministers and leading sports stars.
Doughty, 54, a lifelong Forest fan, saved the club from administration with an STG11 million ($A16 million) takeover in 1999.
He quit as chairman of the Championship side in October following the sacking of former England manager Steve McClaren. Doughty was replaced in that role by former Forest manager Frank Clark but remained the club’s owner.
“It is with enormous sadness that Nottingham Forest announce the death of the club’s owner Nigel Doughty,” the club said in a statement.
“Mr Doughty, who was 54, was found dead earlier today in his gym at his home in Skillington, Lincolnshire.
“The club would like to appeal for the privacy of Mr Doughty’s family to be observed at this sad time. The club will be making no further comment.”
Lincolnshire Police said there were no suspicious circumstances surrounding his death.
Forest, who lifted the European Cup in 1979 and 1980 under manager Brian Clough, are languishing in the Championship relegation zone and face a local derby at east Midlands arch rivals Derby on Sunday.
Doughty gave at least STG3.5 million ($A5.2 million) to the opposition Labour Party over the past seven years and was on its board of assistant treasurers.
Former British prime minister Tony Blair said: “Nigel was a wonderful man, generous, committed and decent.
“He was a great supporter of Labour and of many charitable causes worldwide. He will be sorely missed.”
Fellow former Labour PM Gordon Brown, a family friend, added: “Nigel Doughty will be remembered as a gentle giant; a good, soft-spoken man with a deep commitment to public service who, from his great success in business, became one of our country’s most generous benefactors.
“He will be mourned by many who never knew him or met him but were beneficiaries of his commitment to good causes.”
Forest forward Matt Derbyshire said: “I can’t believe the sad news, my thoughts go out to his family.”
Team-mate Garath McCleary praised Doughty, saying: “He has done so much for Forest, which was not always best appreciated. My thoughts are with his family.”
Former Forest and England striker Stan Collymore also passed on his condolences.
Beyond football, former world No.1 golfer Lee Westwood, who hails from Nottinghamshire, tweeted: “Terrible news to hear that the Forest chairman Nigel Doughty has died”.
Nottinghamshire and England cricketer Stuart Broad – a Forest fan – added: “He was a lovely man and did a huge amount for Forest”.