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 sapping minutes on Friday.
The former world No.1 again had his left thigh heavily strapped after injuring 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 opening 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.
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 remains level with Margaret Court on 24 grand slam victories. (James Ross/AAP PHOTOS)
Zverev's victory, which came when Djokovic quit after losing the tiebreaker 7-5, propelled the 27-year-old second seed into his maiden Australian Open final, and the third grand slam title match of his career.
The world No.2 lost the 2020 US Open final to Dominic Thiem as well as last year's French Open decider to Alcaraz.
But Djokovic's future remains unclear.
Turning 38 in May, he had been bidding to win an unprecedented 25th grand slam singles crown at Melbourne Park, having been level with Margaret Court on 24 since the 2023 US Open.
Now the super Serb admits he doesn't 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)."
Not how we wanted your campaign to end, — #AusOpen (@AustralianOpen) @djokernole.Thank you for another wonderful Australian summer. Well played and best wishes for a speedy recovery.#AO2025 pic.twitter.com/d5VJ6YNBeNJanuary 24, 2025
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.
The German offered his sympathy to Djokovic and urged the Rod Laver Arena crowd to show respect towards the living legend, after some spectators booed the seventh seed on his withdrawal.
"I know that everybody paid for tickets and everybody wants to see hopefully a great five-set match and everything but you've got to understand," Zverev said.
"Novak Djokovic is somebody who has given this sport for the past 20 years absolute everything of his life.
"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 really, really show some love for Novak as well."
Zverev called for respect for Djokovic after progressing to his third grand slam final. (James Ross/AAP PHOTOS)
Zverev was as surprised as everyone when Djokovic called it quits.
"I actually thought it was quite a high-level first set," he said.
"But, I mean like, of course, there are some difficulties and the longer you continue playing then maybe the worse it gets.
"In the tiebreak, maybe he was not moving as well as in the entire first set but I thought we had extremely long rallies, extremely difficult, physical also rallies.
"In the tiebreak, I did see him struggle maybe a bit more."
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