Doctors have again operated on Seve Ballesteros to reduce swelling after removing a brain tumour on Tuesday.
La Paz hospital in Madrid said on Thursday said it would be days before it is known how serious the cancer is.
His considtion is described as stable and he is in an intensive care unit. it is not yet known if the cancer is malignant or benign.
Ballesteros, 51, was taken to hospital last week after suffering dizziness and a brief loss of consciousness.
He won the British Open three times and the US Masters twice.