"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 Madrid's La Paz hospital.
The 51-year-old Ballesteros, who was admitted to the hospital on Monday after briefly losing consciousness, said that he would undergo a biopsy on Tuesday before the doctors decided how to proceed.
"Throughout my career I have been among the best at overcoming challenges on the golf course," Ballesteros said. "Now I want to be the best confronting the hardest challenge of my life, with all my strength, counting on all of you who are sending me encouraging messages."
Ballesteros did not give any more details on the test results - including if 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.
"Now my wish is to ask for respect towards my family and especially my children. We will keep you informed."
The former Ryder Cup star, who won a record 50 times on the European tour, won the British Open three times and the Masters twice before retiring last year due to a long history of back pain.
Many credit Ballesteros' swashbuckling spirit and flare on the golf course for transforming the European game.
The Pedrena native could manufacture shots from just about anywhere, including a memorable one from a parking lot next to the 16th fairway at Royal Lytham & St. Annes on his way to victory at the 1979 British Open.
When the Ryder Cup competition was expanded to include continental Europe in 1979, Ballesteros helped beat the United States in 1985 to begin two decades of dominance. He also captained Europe to Ryder Cup victory on home soil in 1997 at Valdarrama.