Melbourne - Roger Federer paid an emotional tribute to Brad Drewett Tuesday after the men's tennis boss said he was stepping down after being diagnosed with motor neurone disease.
The 54-year-old Australian said he will continue as executive chairman 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 record 17-time Grand Slam champion Federer and Andy Murray.
"It's a very sad situation for all of us. I saw him on Monday and he told me the news. Obviously very emotional," Federer said. "I've known Brad ever since I came on tour and I started to play a bit better.
"He was so influential. He goes so far back and has touched so many people, throughout his career as a player and then also as an executive and then CEO.
"So it's been very hard to see him not doing so well, we wish him the best, of course. I can only thank him for everything he's done already and more."
World number three Andy Murray said he was shocked at the news.
"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.