MADRID, Spain (AP) -- Seve Ballesteros developed a complication following brain tumor surgery, requiring doctors to remove a piece of the golf star's skull to relieve pressure.

The 51-year-old Spaniard was stable but still in intensive care, La Paz Hospital said on Thursday.

A sizable part of the tumor was taken out on Tuesday, although it was not yet known if it was malignant. The hospital said Ballesteros had presented a "decreased level of consciousness by brain swelling."

Part of the skull was removed -- a procedure known as decompressive craniotomy -- to allow room for a swelling brain to expand. Doctors say it is not uncommon after such operations.

Ballesteros, who won three British Opens and two Masters, briefly lost consciousness and on Oct. 6 was admitted to the hospital, where the tumor was discovered. On Sunday, he acknowledged having a tumor and said he faced the "hardest challenge of my life."

Top-ranked tennis player Rafael Nadal, who said he'd been in contact with Ballesteros' family this week, remained confident that he could overcome this setback.

"He has proved to be a very strong man all his life, we know he is one of the great Spanish sportsmen," Nadal said at the Madrid Masters. "He was the best Spanish golfer ever so I just want to send him all my support and strength."

Ballesteros, who won a record 50 tournaments on the European Tour, retired last year because of a long history of back pain and has since concentrated on golf course design.

Ballesteros transformed European golf. After the Ryder Cup 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 victory in 1997 at Valderrama, Spain.

Ballesteros and Jose Maria Olazabal made one of the most formidable partnerships in Ryder Cup history, with 11 wins, two losses and two halves.

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