Responsible for inventing the "Cruyff Turn" -- a football trick still seen across school playgrounds to this day -- the Dutchman also helped to champion the "Total Football" philosophy that made his Ajax and Netherlands sides some of the most revered of all time.
The 68-year-old, who won three consecutive European Cups with Ajax and helped Netherlands reach the 1974 World Cup final, has been undergoing medical tests at a hospital in Barcelona, which uncovered the illness. The examinations are still ongoing.
"To respect the privacy of Johan and his family, and the fact that the examinations have not been finalized, further announcements cannot be made at the moment," a statement from Cruyff's management read.
"We hope that people are willing to respect the privacy of Johan and his family. We will make further announcements when the examinations have been finalized."
A former smoker, Cruyff underwent heart surgery in 1991 during his time as coach of Barcelona -- a club he also played for.
After his operation he took part in an anti-smoking advertising campaign, which had the slogan: "I've had to two addictions in my life: smoking and playing football. Football has given me everything, whilst smoking almost took it all away."
Cruyff came to epitomize football in the 1970s and with his lanky hair and flared jeans, the Dutchman had as much swagger off the pitch as he did on it.
The Dutchman won the Ballon d'Or -- the old European Player of the Year award -- three times in 1971, 1973 and 1974 as he helped Ajax to its hat-trick of European titles in 1971, 1972 and 1973.
He also inspired Netherlands to a first ever World Cup final in 1974 in which the Oranje -- one of international football's most exciting sides in history -- lost to host West Germany. Cruyff received the Player of the Tournament award for his efforts.
The Dutchman also enjoyed success in Spain, where he won the Spanish La Liga title and Spanish Copa del Rey while at Barcelona.
As a coach Cruyff's influence has been almost as great as his playing legacy.
He quickly established himself as a Barcelona legend, guiding a side known as the "Dream Team," due to its flowing style of football, to the club's first ever European Cup in 1992.
With Cruyff as coach, Barcelona won four consecutive Spanish La Liga titles from 1991 to 1994, as well as the European Cup Winners' Cup in 1989 and the Spanish Copa del Rey in 1990.
The Dutchman helped to lay the foundations for an identity still seen today at Barcelona -- a club which has a heavy focus on youth development and prides itself on its defined "tiki-taka" style of play.
Barcelona president Josep Maria Bartomeu and vice-president Susana Monje have both voiced their support for Cruyff.
Cruyff, who also had success in charge of Ajax, was last in a managerial post with Catalonia's unofficial "national" team, while he has held a number of minor roles in the game as well.