"Ray Wilkins is currently being treated at St George’s Hospital, and his condition is critical," the hospital said on its official twitter feed on Saturday.
"His family have asked for privacy at this time, and we are tweeting this update with their agreement."
His wife was quoted as saying he had suffered a cardiac arrest and had to be put in an induced coma.
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The 61 year-old Wilkins won 84 caps for England between 1976 and 1986.
He played more than 150 times for each of Chelsea, Manchester United and Queen's Park Rangers, with shorter spells abroad for AC Milan and Paris Saint-Germain.
In a 20-year coaching career he was manager of QPR, Fulham and the Jordan national team, and assistant manager in two spells at Chelsea.
(Reporting by Steve Tongue; editing by Ken Ferris)
