Melbourne - Men's tennis boss Brad Drewett on Tuesday said he was stepping down after being diagnosed with motor neurone disease, in a sudden announcement that prompted a wave of tributes and sympathy.
The 54-year-old Australian said he will continue as executive chairperson and president of the Association of Tennis Professionals (ATP) until a replacement is appointed.
"It has been a privilege to serve as executive chairperson and president of the ATP, an organisation that I've been a part of for more than 35 years since I became a professional tennis player," Drewett said in a statement.
"I hold the ATP very close to my heart and it's with sadness that I make the decision to enter this transition period due to my ill health."
The news, on day two of the Australian Open, prompted expressions of sympathy from well-wishers including Roger Federer, who called it "very sad news".
"Brad has become a good friend of mine over the years and this is very sad news for all of us at the ATP and the entire tennis community," the world No 2 said in the ATP statement.
"He is well liked and respected by everyone and has done a tremendous job in leading the ATP over the past 12 months, overseeing some major initiatives and a record-breaking year in 2012.
"His dedication and service to the sport over the years has been truly admirable and he has been a central figure in helping to grow the ATP product across the globe.
"Our thoughts are with him and his family during this difficult time."
World No 3 Andy Murray said he was shocked.
"It's obviously very shocking news. Very sad. He's done a very good job for the tour," he said.
"He's done a good job of bringing the tournaments together and arranging the meetings we had with the slams. He's definitely had an impact in the time he's been working there.
"It's a big shame to hear something like that happen. Hope he's okay."
Stacey Allaster, head of women's governing body, the WTA, said her thoughts were with Drewett.
"We know he will fight this terrible disease every step of the way, and have our full support for whatever he needs," said Allaster.
Tennis Australia and the Grand Slam Committee, which governs the sport's four major tournaments, also paid tribute.
"Brad's long-standing commitment to the sport marks him as a true member of our tennis family and we wish him well in the fight ahead," the committee said in a statement.
Drewett won two singles titles in the early 1980s during his playing career. Since becoming ATP chief last year, he was instrumental in gaining increased prize-money for players.
Motor neurone disease, also known as Lou Gehrig's disease, is incurable. The life expectancy after diagnosis is normally three to five years.