Federer considers Drewett a friend. The 54-year-old, who ran the ATP's international group operations out of Sydney until taking over the head London-based role last January, will continue his current duties on an interim basis while the ATP board of directors begins the search for his successor.

''I saw him yesterday and he told me the news. Obviously very emotional,'' said Federer, the ATP player council president, after his first-round win over Benoit Paire.

''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, so we wish him the best, of course. Can only thank him for everything he's done already and more. I'm sure he's going to stay on for a bit more and do more work, so we thank him for that. Obviously it's tough. I worked with him very closely, especially the last few years now, and he deserved to be CEO and chairman.''

The condition, also known as Lou Gehrig's disease or amyotrophic lateral sclerosis, affects the nerve cells in muscles, affecting movement, speech, breathing and swallowing. The muscles gradually weaken and waste, meaning that the average life expectancy is two to three years from diagnosis. Drewett has struggled with his speech for more than a year.

''It has been a privilege to serve as executive chairman 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.''

A key figure in the recent player-driven campaign for increased prizemoney at the grand slams, Drewett's 35-year history with the ATP began as a player, then ATP player council member and board member.

He was a former top 40 singles and top 20 doubles player, a two-time Australian Open junior champion and on his grand slam debut in 1975 became the tournament's third-youngest quarter-finalist, aged 17 years and five months. His first administrative post with the men's tour was as chief executive of the international region.

''It is with great sadness that we receive the news about Brad Drewett's illness,'' said a joint statement from Tennis Australia's chief executive Steve Wood and president Steve Healy. ''Brad's incredible contribution to the game in Australia and worldwide is obvious to all. For more than three decades he has been a much loved member of the Australian tennis family.''