Defending champion Novak Djokovic faces a fitness battle to continue in the Australian Open after suffering what he described as a "muscle tear" during a five-set win over Taylor Fritz on Friday.
The 33-year-old, seeking a record-extending ninth title in Melbourne, was cruising after winning the opening two sets of his third-round clash but a slip at 1-1 in the third set almost derailed his progress.
Djokovic disappeared off Rod Laver Arena for treatment and needed further attention during the third set.
His hopes looked to be dashed when Fritz won sets three and four but the 17-time Grand Slam winner showed great resolve to dominate the decider with some superbly accurate serving and groundstrokes.
His 7-6, 6-4, 3-6, 4-6, 6-2 win was his 78th career match victory at the Australian Open but whether he will be able to go for No 79 against Milos Raonic on Sunday remains to be seen.
"Right now, I'm ... well, I know it's a tear, definitely, of the muscle," Djokovic said about the issue affecting his right side, which he stated had initially left him unable to move or rotate.
"So, I don't know if I'll manage to recover from that in less than two days. I don't know if I'm going to step out on to the court or not. I am just very proud of this achievement tonight. Let's see what happens."
Djokovic was helped by a break in play midway through the fourth set at around 11.30pm local time, when the fans inside the Rod Laver Arena were told to leave to comply with Melbourne's new five-day Covid-19 lockdown, which was due to start at midnight.
Although he still lost the fourth set, he was able to move more freely in the fifth, in which he dropped only five points on his serve and struck 13 winners.
Djokovic had been riled by the boisterous crowd earlier in the match but after a short break in play to allow disgruntled fans to head for the exits, he revelled in the calm atmosphere.
"I was just going for my shots. I was hitting two first serves and it worked," he said.
"Obviously, with the bad news that we got today, everybody knew that midnight is going to be the deadline. 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.
"Maybe a bit too loud at certain moments."