World No10 Bubba Watson said: "Praying for Seve & his family!!!"
Ballesteros, a successful Ryder Cup captain in 1997, had planned a farewell appearance for British fans at last year's Open at St Andrews in a four-hole Champions Challenge before his health prevented him from travelling.
And at last month's Masters at Augusta, world No4 Phil Mickelson decided on a Spanish menu for the Champions Dinner in honour of the absent Cantabrian.
Ballesteros is held in particularly high affection in this country after winning the Open three times with his swashbuckling style of play.