MELBOURNE — Novak Djokovic said he tore a muscle during a fall in his five-set victory in the Australian Open's third round and might need to pull out of the tournament.

His opponent, American Taylor Fritz, wasn't so sure. He figured Djokovic definitely will be back out there Sunday to continue his pursuit of a ninth championship at Melbourne Park and 18th Grand Slam title overall.

"If he can play like he played in the fifth, I don't see why he wouldn't play," Fritz said. "He'll beat pretty much anyone." 

The No. 1-ranked Djokovic seemed to be cruising along with a two-set lead Friday night when his left foot gave out from under him as he tried to change directions and he slipped awkwardly on the white "MELBOURNE" lettering at the back of the blue court. He took a medical timeout for treatment on his side and later was helped more by a trainer. Fritz got back into the match, before Djokovic eventually won 7-6 (1), 6-4, 3-6, 4-6, 6-2.

When it ended, Djokovic puffed his chest, held his arms out wide and bellowed, his voice echoing through an empty and otherwise silent Rod Laver Arena. The match began with spectators present, but they were forced to leave a little past 11:30 p.m. — about an hour before Djokovic wrapped up his win — because a local COVID-19 lockdown began at midnight. 

During an on-court interview, he was subdued.

And pessimistic.

"I know it's a tear, definitely, of the muscle. So I don't know if I'll manage to recover from that in less than two days. I don't know. I don't know. I don't know if I'm going to step out onto the court or not," said Djokovic, who is supposed to face 2016 Wimbledon runner-up Milos Raonic with a quarterfinal berth on the line.

"I am just very proud of this achievement tonight," Djokovic said. "Let's see what happens tomorrow."

The only man in the draw with more Grand Slam trophies than Djokovic, No. 2 Rafael Nadal, has been complaining about a bad back since last week. Nadal's bid for his men's-record 21st major title — breaking a tie with Roger Federer — continues Saturday in the third round against Cameron Norrie.

Others in third-round action Saturday include No. 4 Daniil Medvedev, No. 5 Stefanos Tsitsipas, No. 7 Andrey Rublev, No. 9 Matteo Berrettini and the last American man in the tournament, unseeded McKenzie McDonald.

In addition to Djokovic-Raonic, the fourth-round matchups slated for Sunday are No. 3 Dominic Thiem vs. No. 18 Grigor Dimitrov, No. 6 Alexander Zverev vs. No. 23 Dusan Lajovic, and No. 20 Felix Auger-Aliassime vs. Aslan Karatsev, a Russian qualifier who is ranked 114th and making his Grand Slam debut.

On Friday, Djokovic's match was halted for about 10 minutes while the crowd was cleared out, which bothered Fritz.

"I mean, to be honest — like, completely honest — it's absolutely ridiculous that at a Grand Slam match, we're asked to leave the court for 10 minutes in the middle of the match," said Fritz, a 23-year-old from California who was seeded 27th. "That shouldn't be a thing at a Grand Slam. … We shouldn't have played tonight if we weren't going to finish the match on time."

No fans will be allowed at the tournament for at least five days. 

"In a way, it's unfortunate for the crowd that we didn't finish the match with them seeing the end. They were enjoying it, certainly," said Djokovic, the champion in Australia each of the past two years. "On the other hand, you know, for me regardless of the crowd in the stands or not, I was just trying to focus on what's going on with an injury and just praying and hoping that somehow it would get better."

After his movement and usually strong returns were clearly hampered in the third and fourth sets, Djokovic began to assert himself more in the fifth.

Things swung suddenly back in his favor with a break to 4-2.

"Looked like he was struggling in the third and the fourth, and he didn't really look like he was struggling in the fifth," Fritz said. "He looked fine in the fifth. Let's be honest."

This setback dropped Fritz's career record in third-round matches at Grand Slam tournaments to 0-6.

"I make (the) third round literally every single Slam. I just want to make it to the fourth round," Fritz said. "Like, it's so tough. I fought so hard and wanted it so bad, and it's just really tough to go out like that."