Earlier this month Ballesteros spoke to his family for the first time since his latest operation, to remove a tumour and reduce brain swelling, on 24 October.
The 51-year-old won 87 titles during his career, including the Open in 1979, 1984 and 1988 and the Masters in 1980 and 1983.
Ballesteros was suffering from an oligoastrocytoma, a tumour composed of two types of brain cell which spreads inside the brain cavity.
He retired from golf last year following arthritic back and knee problems, while doctors discovered an irregular heartbeat when he was admitted to hospital in 2007.
"With the help of God, the neurosurgeons and their teams, and those who are keeping watch over his state of health at the intensive care unit, we trust with unquestioning faith Seve will come out successfully from this hardship," said his family in a statement on Ballesteros's website.
Ballesteros is expected to stay at the Madrid hospital to continue his rehabilitation for some time.
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