Nottingham Forest owner Nigel Doughty was found dead in the gym of his Lincolnshire home, the Championship club revealed on Saturday.
Doughty, 54, quit as Forest chairman in October following the sacking of former England manager Steve McClaren.
He was replaced by former Forest manager Frank Clark but remained owner of the struggling second-tier club, which he saved from administration with an £11 million takeover in 1999.
"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."
Forest, two-time European champions during Brian Clough's reign, are currently languishing in the Championship relegation zone and face a local derby at arch rivals Derby on Sunday.
Forest forward Matt Derbyshire said: "I can't believe the sad news, my thoughts go out to his family," while golfer Lee Westwood, born in nearby Worksop, tweeted: "Terrible news to hear that the Forest chairman Nigel Doughty has died."
Derbyshire's 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."
Nottinghamshire and England cricketer Stuart Broad -- a Forest fan -- added: "He was a lovely man and did a huge amount for Forest."