Ten-time champion Novak Djokovic has sensationally withdrawn from the Australian Open after losing a marathon first set of his semi-final against second seed Alexander Zverev.
Djokovic walked immediately to the chair umpire to say he could not go on after dropping the set in a tiebreaker after one hour and 21 minutes on Friday.
The former world No.1 again had his left thigh heavily strapped after hurting himself in his quarter-final win over Carlos Alcaraz on Wednesday night.
Djokovic said he had a hamstring tear and, while he may have played on had he won the first set, conceded he could not have continued for four or five hours.
"It was going to be a huge uphill battle for me. It was getting worse and worse," Djokovic said.
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The 37-year-old said it was similar to the hamstring injury he nursed while winning his 10th Open title two years ago, after which he revealed a 3cm tear.
Djokovic said he does not know how long he will take to recover, when he will return to the court, or if he will even be back at next year's Open.
"I don't know. There is a chance (I won't be back)," Djokovic said.
"Who knows? I'll just have to see how the season goes. I want to keep going, but whether I'm going to have a revised schedule or not for the next year, I'm not sure.
"I normally like to come to Australia to play. I've had the biggest success in my career here, so if I'm fit, healthy, motivated, I don't see a reason why I wouldn't come.
"But there's always a chance, yeah (that I won't return)."
Zverev's victory, which came after Djokovic quit after losing the tiebreaker 7-5, propelled the 27-year-old German into his first Australian Open final, and third grand slam title match of his career.
In his post-match interview, Zverev urged fans not to boo Djokovic as he exited.
"I know that everybody paid for tickets and everybody wants to see a great five-set match and everything, but you've got to understand Novak Djokovic is somebody that has given the sport for the past 20 years absolutely everything of his life," Zverev said.
"He has won this tournament with an abdominal tear, he has won this tournament with a hamstring tear, if he cannot continue a tennis match it really means he cannot continue a tennis match, so please be respectful and show some love for Novak as well."
World No.2 Zverev lost the 2020 US Open final to Dominic Thiem as well as last year's French Open decider to Alcaraz.
Zverev will play the winner of Friday night's second semi-final between Italy's top-ranked titleholder Jannik Sinner and American world No.20 Ben Shelton.
