MADRID, Spain -- Seve Ballesteros is scheduled to undergo another operation on a brain tumor, La Paz Hospital said in a statement Thursday.
The operation Friday will attempt to relieve pressure on his brain caused by an edema and bleeding that have recently developed.
The remaining parts of the tumor, located in a very deep part of the brain, will be removed in the operation, the statement said.
A study of cells already removed has revealed the tumor is classified as an oligoastrocitoma, a type that affects "cells that cover and protect the nerve cells in the brain and spinal cord," the statement said.
The hospital said the operation is "of great complexity."
Ballesteros was admitted to the hospital Oct. 6, and 10 days later a sizable part of the tumor was taken out.
Part of his skull was removed -- a procedure known as decompressive craniotomy -- to allow room for a swelling brain to expand. Doctors said it was not uncommon after such complex operations.
Ballesteros, who won three British Opens and two Masters, briefly lost consciousness while at Madrid's international airport on Oct. 6 and was admitted to the hospital.
In a personally signed statement from his hospital bed, Ballesteros said he faced the "hardest challenge of my life."
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.