A five-time major winner, including the Masters Tournament in 1980 and 1983, the 51-year-old Ballesteros was set to undergo a biopsy Tuesday before doctors would determine how to proceed. He was admitted to a hospital last Monday after briefly losing consciousness.
"Once I had been able to inform my three children personally and their mother, I can now communicate to you the illness I am suffering from. After an in-depth check up which has been carried out on me in the La Paz Hospital they have detected a brain tumor," Ballesteros said in a statement released by the Madrid hospital.
Ballesteros did not give any more details on the test results. It was unknown whether the tumor was benign or malignant.
"I have always shown my solidarity with those people who face illness, including those whose (illnesses) are much worse than mine," said Ballesteros, who was also admitted to a hospital last year when doctors discovered an irregular heartbeat.
Ballesteros played his whole career as if he had something to prove and the effects have shaped European golf today.
The swashbuckling Spaniard was well known for being able to manufacture a shot from just about anywhere, a feat that earned him the title "Car Park Champion" at the 1979 British Open. He found the green from a parking lot next to the 16th fairway at Royal Lytham & St. Annes before sinking a long birdie putt on his way to his first major title. During that final round, he used his driver only nine times and hit the fairway once.
Jose Maria Olazabal, who visited Ballesteros after playing at the Madrid Masters on Sunday, said that his former Ryder Cup partner appeared in good physical shape.
Ballesteros, who won a record 50 times on the European Tour, also won the British Open in 1984 and 1988 before retiring last year because of back pain. He has since focused mostly on golf course design.
Many credit Ballesteros' spirit and flare on the golf course for transforming the European game.
When the Ryder Cup competition was expanded to include continental Europe in 1979, Ballesteros helped beat the U.S. in 1985 to begin two decades of dominance. He also captained Europe to Ryder Cup victory on home soil in 1997 at Valderrama.