The family of Seve Ballesteros, the most exhilarating golfer of his generation, were at his hospital bed last night amid reports that he was gravely ill with a brain tumour.

The Spanish golfer has been in intensive care in Madrid since collapsing on Monday.

His family yesterday asked staff at the Hospital de la Paz not to release any further information about his condition. Security guards have been deployed at the hospital to prevent unauthorised access.

Ballesteros, 51, collapsed and lost consciousness at Barajas airport on Monday and was rushed to hospital. The three-times British Open winner, who electrified the sport in the 1980s with his inventive and daring play, released a statement from his hospital bed on Thursday saying that he was awaiting the results of medical tests.

There has been speculation that the golfer, who is separated from his wife Carmen Botin, the mother of his three children, has been battling a serious medical condition for some time.

He denied suffering from periods of depression when he announced his retirement at The Open in Carnoustie last year. He also refuted reports that he had tried to commit suicide with an overdose of pills after the death of his girlfriend, Fatima Garlaza, in a car crash. He had, he said, been admitted to hospital with a heart problem. Tests later revealed that he had an irregular heartbeat.

Ballesteros said at Carnoustie that he had wanted to deny the unfounded reports of his ill-health to the British public face-to-face. “There was always a good feeling, always a good chemistry between us. Most of my wins were down to them,” he said.

Hopes that the golfer was making a recovery rose on Thursday when he released a statement through his family. In it he said: “Thank you for your concern for my health and for your messages of support . . . I would like to inform you that I feel well. I am awaiting the result of the tests which they are carrying out on me. Many thanks to all.”

It is believed that his condition deteriorated yesterday, however.

An official at the Madrid Masters event said that a statement on Ballesteros’s health had been expected at lunchtime yesterday but had not materialised. “One rumour is that he has a [brain] tumour but nothing has been confirmed,” he said. “Some are saying they are doing tests to find out whether he can have surgery or not.”

Hospital staff would only say yesterday that they were finalising tests on his condition. They were expected to be complete by last night.

Ballesteros won 87 titles during his career, including The Open in 1979, 1984 and 1988 and the Masters in 1980 and 1983. He also played an inspirational role in the Ryder Cup, winning 20 points from 37 matches, as well as captaining Europe to victory at the Spanish course of Valderrama in 1997.

The British golfer Colin Montgomerie said yesterday that he was speaking for all his fellow professionals when he wished Ballesteros a speedy recovery.

“What we are hearing puts everything into perspective in a heartbeat,” said Montgomerie, who played under Ballesteros at Valderrama.

“Seve has this fighting spirit, this never-say-die approach. He has come back from four down with nine to play to defeat both Paul Azinger and Raymond Floyd and he has done much the same against me a couple of times. His great attitude and his passion should serve him well now.”