Former England and Aston Villa defender Ugo Ehiogu has died in hospital aged 44 following a cardiac arrest, Tottenham Hotspur said on Friday.
Ehiogu, who worked as Tottenham's under-23 coach, had collapsed at the North London club's training ground on Thursday.
He passed away in the early hours of Friday, the Premier League title contenders said in a statement.
"Words cannot express the shock and sadness that we all feel at the Club," said Tottenham's head of coaching and development John McDermott. "Ugo's immense presence will be irreplaceable."
Ehiogu, who started out as a trainee at West Bromwich Albion but spent most of his career at Aston Villa, was capped four times by England.
He would doubtless have won more caps but for injury and competition from younger defenders like Rio Ferdinand and John Terry.
As well as playing more than 200 times in nine years for Villa, London-born Ehiogu played 126 games for Middlesbrough after becoming their then-record signing for eight million pounds ($10.24 million) in 2000.
He won the League Cup with both Villa and Middlesbrough.
Also playing for Rangers in the Scottish Premier League, Ehiogu scored a winner against Celtic in the 2007 Old Firm derby with a spectacular overhead kick that was later voted the club's goal of the season by fans.
He ended his professional career at Sheffield United in 2009 and joined Tottenham's coaching staff in 2014 after a spell with the England under-20 side.
Championship side Villa said they would be holding a minute's applause before their home derby with Birmingham City on Sunday with both sets of players wearing black armbands as a mark of respect.
Tributes poured in from across the soccer community expressing shock and sadness.
"Everyone at the FA is devastated to hear the news that Ugo Ehiogu has sadly passed away," the Football Association said in a statement.
"This is an absolute shock, to think this could happen to a man of his fitness and age. It is devastating, crazy," former Villa team mate Lee Hendrie told Sky Sports television.
"He was such a character, bubbly and would help anyone. He was a great guy to have around and never had problems with anyone. He was a gentle giant."