Australia's Brad Drewett, the president of the ATP, died on Friday at the age of 54 following a battle against motor neurone disease, the governing body of men's tennis announced.
"The ATP is deeply saddened to announce that Brad Drewett passed away at his home in Sydney, Australia, earlier today," said an ATP statement.
"Brad, who served as ATP executive chairman and president since January 2012, had been suffering from motor neurone disease.
"Our thoughts are with Brad's family on this extremely sad day for them, the ATP and the entire international tennis community. He will be sorely missed by all."
Spanish star Rafael Nadal was amongst the first to pay tribute to the Australian.
"A very sad day for the world of sports and tennis in particular. Our president Brad has passed away. Rest in peace," said Nadal on his Facebook page.
A period of silence was observed at the draw for the Madrid Masters which starts on Saturday.
Drewett said in January that he was stepping down from his role with the ATP after being diagnosed with the incurable disease.
However, he added at the time that he would continue as executive chairman and president of the ATP until a replacement was appointed.
"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.
"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."
Drewett won two singles titles in the early 1980s during his playing career.
He also rose to number 34 in the world rankings.
Since becoming ATP chief last year, he was instrumental in helping to secure a larger share of prize money for the journeymen of the sport who more often than not fall at the first hurdle of the four Grand Slams.
Stacey Allaster, the head of the WTA, described Drewett as a "great" administrator.
"Brad's contributions as a player and visionary leader make him one of the greatest in making tennis the popular, worldwide sport it is today," she said.
"The recent prize money increases with the Grand Slams are perfect examples of Brad's brilliant strategic management, and another example of how much he cared about our athletes and the sport's long-term growth."
International Tennis Federation (ITF) president Francesco Ricci Bitti also praised the Australian.
"The ITF family is deeply saddened to learn of the death of Brad Drewett," said the ITF chief.
"Brad was a valued friend and colleague to many of us here at the ITF, and we were very happy to support him during his various roles at the ATP, most recently as Chairman.
"His knowledge, experience and enthusiasm will be a great loss to the whole sport. We send our deepest sympathies to Brad's family and to everyone at the ATP during this very sad time."
Tennis Australia (TA) said Drewett was an "inspirational leader" for tennis.
"Brad has always been a much loved friend and colleague to the Australian tennis family as well as an inspirational leader of our sport on the world stage. He will be sorely missed," TA said in a statement.
Motor neurone disease, also known as Lou Gehrig's disease, is incurable. The life expectancy after diagnosis is normally three to five years.