Jack Nicklaus, the only man to win more majors than Tiger Woods, was shaken by the news of his fellow American golf great's car crash.
Nicklaus reacted on Tuesday to news coming out of California that Woods had been taken to hospital and then to surgery after suffering serious leg injuries.
The 18-time major winner said he hoped Woods would soon be back to full health.
Emergency services were called to the scene of the single-car crash shortly after 07:00 local time.
Woods' agent, Mark Steinberg, said the 45-year-old suffered "multiple" Injuries to his legs. The cause of the crash was not initially clear.
Nicklaus and wife Barbara expressed worry about Woods, who won his 15th major at the 2019 Masters, his first victory of such magnitude in 11 years.
The 81-year-old Nicklaus wrote on Twitter: "Barbara and I just heard about Tiger's accident, and like everyone else, we are deeply concerned.
"We want to offer him our heartfelt support and prayers at this difficult time. Please join us in wishing Tiger a successful surgery and all the best for a full recovery."
Augusta National, home to The Masters, a tournament that Woods has won five times, called the news of his accident and hospitalisation "upsetting".
In a statement posted to Twitter, club chairman Fred Ridley said: "Tiger Woods is part of the Augusta National family, and the news of his accident is upsetting to all of us. We pray for him, for his full recovery and for his family during this difficult time."