Novak Djokovic set for scan Tuesday as French Open defence hangs in the balance

The world number one limped into the quarter-finals after defying a knee injury to come through the longest Roland Garros match of his career.

Djokovic defeated Francisco Cerundolo â- in another five-setter â- 6-1 5-7 3-6 7-5 6-3 in four hours and 39 minutes.

He said: "I guess we'll do some more screening and tests and check-ups tomorrow, as well.

"We have done some with the doctor right now after the match. Some positive news but also some maybe concerns, so let's see tomorrow. I can't tell you more about it at the moment."

Djokovic blamed the slippery court for the injury he appeared to sustain at the start of the second set.

He began grimacing and rubbing his right knee shortly after taking the first set and required a medical time-out at 2-1 down in the second.

Djokovic was heard telling the physio: "I screwed up my knee. I'm slipping and sliding all the time."

Four games later he complained to a tournament supervisor about the state of the court, saying: "I'm telling you as a player, it's not OK."

When the official told Djokovic the grounds people felt the surface was fine, the Serbian snapped: "They know better than me the court is good or not?"

The 37-year-old took medication again after Argentinian 23rd seed Cerundolo levelled the match, finally converting a break point at the 13th attempt.

Cerundolo also took his 14th at the start of the third set as Djokovic continued to hobble between points.

The 24-time grand slam champion, whose five-set match against Lorenzo Musetti finished after 3am on Sunday morning, appeared to be running on empty and chuntered with his team in the players' box, occasionally appearing to suggest he was ready to give up.

Yet he retrieved a break in the fourth set and then took the match to a decider, letting out a huge roar as Cerundolo dunked a forehand into the net.

And he did not appear too injured when he dived to get to a volley at the net, almost going full splits before landing on his stomach on his way to winning another remarkable match.

Afterwards, Djokovic said: "At one point I didn't know, to be honest, whether I should continue or not with what's happening.

"I got medications and then after the third set was done, I asked for more medications and I got them.

"That was the maximum dose that kicked in, as I heard now from the doctor after 30 to 45 minutes, which was just about the end of the fourth when things started to really improve for me. I started to feel less limitations in my movement.

"Basically the whole fifth set was almost without any pain, which is great, you know. But then the effect of the medications will not last for too long, so I'll see.

"I'm glad that I was able to play the fifth set and last three, four games of the fourth without feeling that pain that I felt for two-and-a-half sets. But yeah, you never know what will happen tomorrow."

Assuming he is fit, Djokovic will face two-time runner-up Casper Ruud in the last eight.

Norwegian seventh seed Ruud defeated American Taylor Fritz 7-6 (6) 3-6 6-4 6-2.

READ MORE: Novak Djokovic survives five-set thriller to march on to French Open quarters