Novak Djokovic was sensationally disqualified from the US Open after accidentally hitting a line judge with a ball struck in annoyance.

The top seed and 17-time grand slam champion had just dropped serve to trail Spanish opponent Pablo Carreno Busta 6-5 in the opening set of their fourth-round match on Arthur Ashe Stadium.

Djokovic, who had missed three set points at 5-4 before hurting his shoulder in a fall, hit a ball behind him without looking which struck a female line judge in the throat.

The line judge collapsed to the court and could be heard gasping for air as Djokovic rushed over to check on her condition.

Djokovic could be heard pleading his case during lengthy discussions with tournament referee Soeren Friemel and grand slam supervisor Andreas Egli, but the officials’ mind was made up.

A statement from tournament organisers read: “In accordance with the Grand Slam rulebook, following his actions of intentionally hitting a ball dangerously or recklessly within the court, or hitting a ball with negligent disregard of the consequences, the US Open tournament referee defaulted Novak Djokovic from the 2020 US Open.”

The decision will send shockwaves through the sport. Djokovic won his 17th slam singles title in Australia and was an overwhelming favourite to make it 18 in New York having not lost a match all season.

It was unquestionably an accident, and the ball was not struck particularly hard, but it is not the first time Djokovic has flirted with such a scenario.

At the French Open in 2016 he threw his racket and nearly hit a line judge, while later that season he reacted with annoyance when questioned about a warning for hitting a ball angrily into the crowd during the ATP Finals.

Speaking at his post-match press conference, Carreno Busta had sympathy for Djokovic but felt it was the right decision.

He said: “I was in shock. I never expected this moment playing against Novak. So it was a tough moment also for me.

“I think this was not intentional. I don’t think that any one of us, of the players, do this kind of thing intentionally. It’s just the moment. The rules are the rules. The referee and the supervisor do the right thing, but it is not easy to do it.”

Djokovic is not the first player to be defaulted in similar circumstances, but for it to happen at a grand slam and as the tournament favourite is an extraordinary situation.

Canadian Denis Shapovalov was defaulted during a Davis Cup tie against Great Britain in 2017 after smashing a ball in anger that hit umpire Arnaud Gabas in the eye.

Tim Henman, meanwhile, was disqualified from Wimbledon 25 years ago for hitting a ball girl with a ball during a doubles match, while David Nalbandian kicked an advertising hoarding during the Queen’s final in 2012, injuring a line judge, and was defaulted.

Speaking on Amazon Prime, Henman said: “It’s a massive shock. There’s no doubt that it’s the right decision. It’s amazing for me to talk about this because it happened to me at Wimbledon in 1995. It was that moment of frustration, hit the ball away when I wasn’t looking and I hit a ball girl in the ear.”

Djokovic will forfeit his prize money and ranking points, and he will face a further fine for opting to leave the site immediately rather than explain himself in a press conference.

That decision earned strong criticism from Henman, who said: “There’s no doubt he’s made a mistake, which was an accident on the court.

“Unfortunately he’s compounded the error because he needs to face up to it, apologise and accept that he made a mistake. By then, in essence, running away from it, it’s going to go on longer.”

It is a remarkable end to a contentious summer for Djokovic, who earned criticism from inside and outside tennis when the exhibition Adria Tour he organised in the Balkans resulted in several players and coaches, including Djokovic, testing positive for Covid-19.

On the eve of the US Open, meanwhile, Djokovic left his role as head of the ATP Player Council to set up a rival player organisation.

His biggest critic among his fellow players has been Nick Kyrgios, who weighed in from Australia.

He wrote on Twitter: “Swap me for jokers incident. ‘Accidentally hitting the ball kid in the throat’ how many years would I be banned for?”

Djokovic’s disqualification means that, for the first time since Marin Cilic won the US Open title in 2014, there will be a new men’s grand slam champion.

Second seed Dominic Thiem, a three-time losing slam finalist, is now the highest-ranked player remaining.

Fifth seed Alexander Zverev, who eased into the last eight in New York for the first time with a 6-2 6-2 6-1 victory over Alejandro Davidovich Fokina, said he was in shock.

The German said: “He hit a tennis ball. It’s very unfortunate that he hit the line judge, and especially where it hit her. There is a rule in place for it. I think the supervisors and all of them are just doing their job. But very unlucky for Novak.

“I don’t know what to say. I’m a little bit in shock right now.”

Zverev becomes one of the new contenders for the trophy, and he said: “Now I think is the time where it gets really interesting. I know who I can play. I know who the rest of the guys can play. We’ll see where we go from here.”