Spectators booed an injured Novak Djokovic as he left the court in Rod Laver Arena after quitting one set into his Australian Open semifinal against Alexander Zverev on Friday.

Dealing with a what he said was a torn muscle, Djokovic lost the opener 7-6 (5) when he put a forehand volley into the net, then began shaking his head and immediately walked over to shake Zverev's hand. The 37-year-old Djokovic packed up his equipment and walked off toward the locker room, pausing to respond to the jeers by giving two thumbs-up.

At his news conference, Djokovic said the pain in his taped left leg was “getting worse and worse.” He hurt it during his quarterfinal victory over Carlos Alcaraz on Tuesday night.

“I knew," Djokovic said, "even if I won the first set, it was going to be a huge uphill battle for me.”

He was bidding for an 11th championship at the Australian Open and record 25th Grand Slam title overall.

But this is the second time in the past four major tournaments he was unable to finish because of an injury: He withdrew from last year's French Open before the quarterfinals because he tore the meniscus in his right knee during a match.

Djokovic underwent surgery in Paris and, less than two months later, reached the final at Wimbledon, then won a gold medal for Serbia at the Paris Olympics.

The No. 2-seeded Zverev reached his first title match at Melbourne Park and on Sunday will face the winner of Friday’s second semifinal between No. 1 Jannik Sinner of Italy, the defending champion, and No. 21 Ben Shelton of the United States. (AP)