Novak Djokovic slides at the net for a forehand against Francisco Cerundolo. GETTY IMAGES

Novak Djokovic cast doubt over his French Open hopes after admitting he needed anti-inflammatory medication to treat a knee injury as he pulled off another astonishing escape in a five-set victory over Francisco Cerundolo on Monday. The world number one outlasted Argentine 23rd seed Cerundolo 6-1, 5-7, 3-6, 7-5, 6-3 for his record 370th win in a Grand Slam match as he reached a 15th consecutive French Open quarter-final.

Whether he takes to the court against Casper Ruud, the player he defeated in last year's Roland Garros final, remains to be seen after Djokovic said he would undergo medical tests to determine the extent of the damage to his right knee.

"I don't know what will happen tomorrow or after tomorrow if I'll be able to step out on the court and play. You know, I hope so. Let's see what happens. I guess we'll do some more screening and tests and checkups 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." said Djokovic.

After a four-hour, 29-minute win over Lorenzo Musetti that ended at 3:07am on Sunday morning in the previous round, the 37-year-old Djokovic was again tested to his physical limits while being impeded by a balky knee. The Serbian rolled through the opening set but a slip in the third game of the second led to Djokovic taking a medical timeout, and he repeatedly received treatment at subsequent changeovers.

Cerundolo, attempting to reach his first quarter-final at a major, threatened to spring an upset as he capitalised on Djokovic's discomfort to move two sets to one in front. The Serbian had already complained about the state of the clay in his match against Musetti, calling for it to be swept at more regular intervals. He again took aim at the court for "screwing up" his knee and looked to be heading for his earliest French Open exit since 2009 when Cerundolo surged 4-2 ahead in the fourth set.

As he has done countless times, Djokovic displayed his immense powers of recovery to retrieve the break of serve, holding his own in the next game before unleashing a bellowing roar to whip up a crowd that sensed the three-time French Open winner was not done just yet.

'Maximum dose'

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

"I got the 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 doctor after 30 to 45 minutes, which was just about the time kind of end of the fourth when things started to really improve for me."

Djokovic saved a break point to nudge 6-5 ahead and Cerundolo eventually was the first to blink, the top seed capitalising on a fourth set point to force a decider.

It felt almost inevitable Djokovic pinched a break to open the fifth set. Cerundolo did not go away though, scrambling his way back on serve before Djokovic again vented his ire at the court conditions after an awkward tumble.

"Well done, supervisor and everybody," he said sarcastically. "Not slippery at all."

An attempted passing shot from Cerundolo had Djokovic at full stretch doing the splits, an indicator of the tremendous quality still produced from both players despite a gruelling battle that spanned four hours and 39 minutes. Djokovic pounced on his opportunity when it arrived in the eighth game, ripping a forehand winner that clipped the baseline to earn the vital break before he sealed another incredible victory.

"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," said Djokovic.

For Cerundolo, so close to the biggest win of his career, it was an agonising reminder of Djokovic's enduring greatness.

"He always finds a way to come back and play his best tennis at the toughest moments and at the end of every match," said Cerundolo.

"I did my best. I was so close, but I couldn't win it. He show again why he's the best."