Novak Djokovic risking damaging his body at Australian Open

Djokovic admitted that he would have pulled out of any tournament other than a grand slam but the incentive of trying to win a ninth title in Melbourne and 18th overall is stronger than the pain.

The 33-year-old, who became the second player after Roger Federer to win 300 grand slam matches, declined to confirm whether he had suffered a tear, as he suspected on Friday.

He said: "Mentally I think you have to accept that I did come into the match knowing that I'll probably feel pain all the way through, which was the case. But the level of the pain was bearable, so I could actually play. And it was kind of going on and off a little bit during the match.

"But I somehow managed to find a way and win, and that's what matters the most. Now I've got another 40 hours or something like that until the next match, which is great about grand slams.

"Most likely I won't be training tomorrow and just, again, going back to recovery routine and hoping that things will get better. It's kind of a gamble, that's what the medical team told me. It's really unpredictable, you can't know what's going to happen with you once you're on the court.

"It could cause much more damage than it is at the moment, but it also could go in a good direction. So that's something that I don't know, and I don't think I will also know until I stop taking painkillers.

"As long as I'm with high dose of painkillers, I still can bear some of the pain. But the tricky thing with the painkillers is that they kind of hide what's really happening in there, so you might not feel it, but then the big damage might be done.

"But I'm fine with whatever is happening post-tournament, because I'm going to take time off to heal properly before I step on the court again.

"I have talked a lot with my own medical team and also the medical team of the Australian Open. They all share the opinion that there is a slight, very slight, chance that I will make a significant damage that would take me out of the tour for some extended period of time.

"But they don't think it's going to be very significantly worse that it's going to jeopardise my entire season."

Djokovic's next match will come on Tuesday against sixth seed Alexander Zverev, who was a more comfortable 6-4 7-6 (5) 6-3 winner over Dusan Lajovic.

The top seed added: "I'm just hoping that it's going to go in the right direction, that I didn't damage it, whatever is happening in there, too much and kind of feel even 10 per cent better than I did today. And if that's the case, I like my chances."

Third seed Dominic Thiem became the biggest casualty of the tournament so far with a meek defeat by Grigor Dimitrov.

Thiem battled back from two sets down to beat Nick Kyrgios on Friday and it appeared that effort had taken it out of the Austrian, who led Djokovic by two sets to one in the final last year before winning his first grand slam title at the US Open.

This match could not have been more different to Friday's clash, which was played in a raucous atmosphere, and the empty stadium matched Thiem's demeanour as he slumped to a 6-4 6-4 6-0 loss.

Thiem cited "some little physical issues" but said: "I don't want to find any excuses. But the thing is that I'm also not a machine.

"I mean, sometimes I would like to be, but there are really, really bad days. As soon as you're not 100 per cent there on the court on this level, then results like this come up, and that's exactly what happened today."

There, the Bulgarian will play this week's surprise package, qualifier Aslan Karatsev, who continued his remarkable run with a 3-6 1-6 6-3 6-3 6-4 victory over 20th seed Felix Auger-Aliassime.

At 27, Russian Karatsev has spent his whole career in the lower reaches of the sport, never breaking the top 100 or playing in the main draw of a grand slam until this week.

He is the first debutant to reach the quarter-finals of the men's singles at a slam since Alex Radulescu at Wimbledon in 1996 and the first qualifier to make the last eight in a decade.