(CNN) -- Golf legend Seve Ballesteros is due to undergo a biopsy for a brain tumor Tuesday before doctors determine how to proceed with his treatment.
Seve Ballesteros announced his retirement from competitive golf at last year's British Open.
It is not yet unknown whether the tumor is benign or malignant.
The five-time major winner, who has been in Madrid's Le Paz hospital since collapsing last Monday, has said that he faces the "hardest challenge" of his life.
"I inform you that after an exhaustive check, that was realized at Hospital La Paz, a brain tumor has been detected," Ballesteros, 51, said in a statement Sunday.
"Throughout my career I have been among the best at overcoming challenges on the golf course. Now I want to be the best confronting the hardest challenge of my life, with all my strength."
Ballesteros has been undergoing tests since being admitted. A statement by the hospital Friday revealed Ballesteros had suffered "a partial epileptic fit" but said he had left intensive care and was in "a stable condition."
The former Ryder Cup captain, who won a record 50 times on the European tour, won the British Open three times and the U.S. Masters twice before retiring last year after battling back problems.
Ballesteros was also admitted to a hospital last year, and doctors discovered an irregular heartbeat.
Fellow Spanish golfers Jose Maria Olazabal and Miguel Angel Jimenez reacted to the announcement by wishing Ballesteros a speedy recovery.
Ryder Cup partner Olazabal, who visited Ballesteros in hospital, said he was "confident" he would recover, adding: "While I'm rightly worried, I thought Seve seemed very well. We were talking for a good while. I wish him a speedy recovery."
Former European Ryder Cup captain Tony Jacklin added: "At his best Seve was the best and the man who did more for golf than anyone else in Europe," said former two-time major winner Jacklin.
"He was our Arnold Palmer and people just love to see him play."
Ballesteros came to prominence by winning the 1979 British Open at Royal Lytham, famously being dubbed the "car park champion" after a miraculous recovery shot from among the vehicles at the Lancashire course.
He also captained Europe to Ryder Cup success over the United States at Valderrama in 1997.
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