Doctors treating Seve Ballesteros say tests have revealed he is suffering from a "grave illness".
Spaniard has been hospitalised since collapsing on Monday
Doctors treating Seve Ballesteros say tests have revealed he is suffering from a "grave illness".
The 51-year-old Spaniard was taken to La Paz hospital in Madrid on Monday after briefly losing consciousness at the city's Barajas Airport, and has since been undergoing tests.
Telegraph.co.uk report that a brain scan has revealed a "grave illness" and, such is the seriousness of his condition, that Ballesteros' family have been summoned to the hospital.
A full medical bulletin is expected to be issued by the hospital on Saturday.
On Thursday, an upbeat Ballesteros had thanked fans for their messages of support.
"I am feeling well," he wrote on his personal website. "I am waiting for the result of medical exams which were carried out on me.
"I wish to personally thank all of those who are concerned about my health condition.
"It is difficult to answer all your messages due to the great number I am receiving. I want you to know they make me feel very good and I feel greatly supported by all of you."
Ballesteros is one of the most influential figures in the history of European golf - he won five majors, the Open three times and Masters twice, during a decorated playing career.
He also compiled an impressive Ryder Cup record, winning 20 points in eight appearance as a player and captaining Europe to victory at Valderrama in 1997.
He collected 87 titles worldwide before knee and back problems forced him to retire in 2007.
