Andy Murray has been "a champion on and off court", said American tennis legend Billie Jean King after the Briton revealed he plans to retire this year.
Murray, who has won three Grand Slams and been a world number one, is being forced to quit because of a hip injury.
And the 31-year-old Scot says next week's Australian Open could be the final tournament of his career.
"So sorry you cannot retire on your own terms," tweeted 12-time Grand Slam winner King.
King was one of many former and current players joining fans in offering their best wishes to Murray following his announcement in Melbourne on Friday.