Spurs and Chelsea legend Jimmy Greaves suffers stroke
A statement from Greaves's family said the 75-year-old, who had a minor stroke in 2012, had been taken ill on Sunday.
Greaves scored 44 goals in 57 England games and a club-record 220 league goals for Tottenham having started his career at Chelsea.
"His wife Irene and four children have asked for privacy during what is a worrying time," added the statement.
"Jimmy had a minor stroke in 2012, but appeared to have made a full recovery.
"He was due to be inducted into the Tottenham Hotspur Hall of Fame on 13 May at a sell-out ceremony at White Hart Lane."
Greaves is fourth on the list of all-time England goal-scorers, behind Sir Bobby Charlton, Gary Lineker and Wayne Rooney.
He was part of England's 1966 World Cup-winning squad but originally missed out on a medal because he was injured during the tournament's group stage.
At the time, only the 11 winning players on the pitch at the end of the final received the award, although football's governing body Fifa changed that practice in 2007.
The World Cup squad players and the families of team manager Sir Alf Ramsey and other backroom staff were finally presented with medals in 2009.