Shanghai, China - Novak Djokovic hailed Rafael Nadal's tennis "legacy" while Carlos Alcaraz said hearing about his fellow Spaniard's retirement was "painful".

Nadal announced Thursday that he will step back from tennis after the Davis Cup finals in November, ending his 22-Grand Slam winning career.

"Your tenacity, dedication, fighting spirit is going to be taught for decades. Your legacy will live forever," 24-time Grand Slam title winner and fellow former world number one Djokovic wrote on Instagram.

Djokovic and Nadal clashed 60 times, with the Serb edging their rivalry 31-29.

They met for the first time at the French Open in 2006 when Nadal triumphed while Djokovic won their last clash, also on the courts of Roland Garros, at the Paris Olympics this year.

Alcaraz, already a four-time major winner at 21, said he had been shocked by Nadal's announcement.

"When I watched it, it was tough to accept it. I was in shock a little bit," said Alcaraz after he was knocked out of the Shanghai Masters in the last eight.

"To see him leave tennis, which is what he loves, is painful, it hurts me," Alcaraz, who will play with Nadal in the Davis Cup in Spain, added.

"I will try to make the most of the time I will be with him... to take advantage of his last moments on court as a professional."

The world number two said Nadal had always been his idol, and it was thanks to him he had become a professional tennis player.

He paid tribute "to everything he has done for tennis, for all the people, for me".

World number one Jannik Sinner commented: "He's an unbelievable person."

The 23-year-old added: "He taught us young players how to behave on the court, how to handle situations on the court. Also to stay humble at the same time, not changing with his success.

"It's tough news for all the tennis world and not only [the tennis world]."

The 38-year-old Nadal is set to end his two decades as a professional with 92 titles and prize money alone of $135 million.

Despite his record-breaking career, Nadal was plagued by injuries, a painful by-product of his all-action, brutal-hitting style.

"Everything has a beginning... and also an ending," said Sinner. "Only he knows how he feels. It's a tough one."

It has been suggested that Sinner's rivalry with Alcaraz could be the new era version of Nadal's 'Big Three' battles with Roger Federer and Novak Djokovic.

Djokovic is still in the Shanghai race, and will take on Czech teenager Jakub Mensik in the quarter-finals on Friday.

"There are a lot of things we can take from them," said Sinner of the three veterans. "We cannot compare us with them. That's impossible, especially in this moment now."

"I think we all were very lucky to see the Big Three playing tennis, and I consider myself very lucky to get to know them also as a person and to learn from them."