Aus Open: Injured Djokovic admits playing on is a gamble

'I didn't know few hours before I stepped on the court tonight whether I'm gonna play or not.'

Wounded Novak Djokovic admits he is taking a gamble by continuing at the Australian Open but says it is worth it to try and claim a record-extending ninth title.

The 33-year-old suffered an injury he described as "a tear" to his right side against Taylor Fritz in the third round on Friday, but was fit enough to beat Milos Raonic 7-6 (4), 4-6, 6-1, 6-4 on Sunday to reach the quarter-finals.

The world number one said he has been having extensive treatment and was on painkillers, but declined to actually explain what the injury was when asked on Sunday.

"I did an MRI (scan), I did everything, I know what it is, but I don't want to talk about it now. I'm still in the tournament," Djokovic told reporters.

"I hope you guys understand that. I don't want to speculate too much about it.

"I didn't know few hours before I stepped on the court tonight whether I'm gonna play or not.

"If I'm part of any other tournament other than a Grand Slam, I definitely wouldn't be playing."

Djokovic occasionally pulled up gingerly against Raonic although he struck the ball with his usual power and precision.

"It's kind of a gamble, that's what the medical team told me. It's really unpredictable," Djokovic said.

"It could cause much more damage than it is at the moment, but it also could go in a good direction. That's something that I don't know, and I don't think I will know until I stop taking painkillers. As long as I'm with high dose of painkillers, I guess I still can bear some of the pain.

"But the tricky thing with the painkillers is that they hide what's really happening in there, so you might not feel it, but then the big damage might be done."

Djokovic will face a potentially tougher test against German sixth seed Alexander Zverev on Tuesday.

"Playing against Sascha is a different matchup, there's probably going to be more rallies, gruelling rallies, exhausting, and it's going to be demanding from my side really from back of the court," Djokovic said.