MELBOURNE, Australia — The grimace on Novak Djokovic’s face after slipping on the white “MELBOURNE” lettering behind the baseline at Rod Laver Arena was enough to suggest the world No. 1’s chances of defending his Australian Open title had just taken a serious hit.

In the third round at Melbourne Park on Feb. 12, Djokovic appeared to be cruising to a straight sets victory over American Taylor Fritz when he fell awkwardly and immediately signaled for the trainer. After undertaking an extended medical timeout, Djokovic returned to the court but appeared significantly hampered in his movement and experiencing serious pain.

The 17-time major champion continually felt around the right side of his abdomen, often attempting to stretch it out between points. He frequently winced as he tracked down balls, giving up on plenty which were struck only a few feet either side of his racket.

In the blink of an eye, Fritz leveled the match at two sets apiece and for the first time in the tournament, there should have been real concern in the Djokovic camp. But the Serbian took the decider 6-2, letting out a giant roar inside center court when he secured match point after three hours and 25 minutes.

“I know it’s a tear of the muscle, definitely,” a deflated Djokovic said immediately after the match. “I don’t know if I’ll manage to recover in less than two days. I’m not sure if I’ll be able to play the next match.”

There has yet to be a proper diagnosis made public about the 33-year-old Djokovic, making his health the greatest mystery over the middle weekend of the Australian Open. The question remains: Would he be able to continue his pursuit of a record ninth crown Down Under, and if not, who would step up and lift the Norman Brookes Challenge Cup?

Much of the speculation following the win over Fritz was that the muscle Djokovic had injured was his right oblique, one of two diagonally-oriented abdominal muscles which run from the rib cage to the anterior trunk, or pelvis. An extreme amount of stress is placed on these muscles in sports which require high rotation, such as tennis. And few, if anyone, in the sport puts more stress and strain on their body than Djokovic.

It takes the average person between eight and 10 weeks to fully recover from a torn oblique, according to Harvard Medical School, but Djokovic had just 48 hours to get himself right for his fourth-round match against 2016 Wimbledon finalist Milos Raonic.

Djokovic was absent from the precinct on Day 6 but returned Sunday for a light gym session, which consisted of some stretching and jogging, before stepping onto John Cain Arena for a practice hit in the afternoon.

A few hours later, he was squeaking and sliding his way around Rod Laver Arena, once again mimicking the defensive qualities of a brick wall and leaving Raonic scratching his head in a combination of disbelief and frustration. Djokovic may have been wearing a large anti-inflammatory patch on the right side of his abdomen, but suddenly he looked more like the player we’ve become accustomed to seeing over the years. Had fans not known about his tumble in the previous match, they never would have guessed he was dealing with a potentially serious injury.

Djokovic needed a little less than three hours to dispatch Raonic 7-6(4), 4-6, 6-1, 6-4, record his 300th Grand Slam victory and move into the quarterfinals at the Australian Open for a record 12th time. How could he possibly manage such a feat with what he believes is a torn oblique?

“The term ‘muscle tear’ can often set off alarm bells, but they are generally scalable and graded from one to three,” ESPN injury analyst Stephania Bell said. “Grade 1, which it could be, suggests little to no structural damage, and while painful, may not adversely affect function in a serious way. Sometimes an athlete can feel a pop or a pull and this is what makes them refer to it as a tear.

“A complete tear would likely prevent him from playing, given the pain and the functional compromise. Things which demand power, such as serving, and things that put the muscles on extreme stretch, such as stretching wide to reach a shot, perhaps even some cross-body shots, would be challenging for Djokovic if he had a full-blown oblique tear.”

After the win against Raonic, Djokovic confirmed he had undergone an MRI in Melbourne and now knows the extent of the injury, although he again didn’t provide any specific details. As long as he is still standing in the tournament, he isn’t eager to share his diagnosis with his rivals.

“I understand that you want to know, but I really don’t want to get into what it is,” he told the press. “It’s not ideal for me. I mean, I have definitely felt better. The combination of painkillers, treatment and some willpower [is getting me through], but I don’t want to talk about it now. It’s irrelevant.”

Djokovic’s ability to recover in such a short period of time and then overcome Raonic is something which has drawn the attention of many around the tour, including Serena Wiliams’ longtime coach, Patrick Mouratoglou.

“Sometimes Novak plays with the mind of an opponent when he’s in trouble,” Mouratoglou told Tennis Majors. “He pretends he’s giving up, and then, boom. He plays again. He’s done that a lot of times in the past.”

Former Australian doubles icon Todd Woodbridge also weighed in, saying, “He’s going to be fine. I’d say to the rest of the field, watch out, because we’ve seen him do these types of things before, have a bit of a hiccup and still win majors.”

It’s not the first time Djokovic has had to fight through an injury at a Grand Slam. At Wimbledon in 2017, he battled a nagging elbow ailment, yet still reached the quarterfinals.

At the 2019 US Open, he withdrew in the fourth round after a left shoulder injury got the better of him, while at last year’s tournament in New York, he fought through neck stiffness to reach the fourth round. He dropped just one set in his first three matches before being defaulted for striking a linesperson in the throat in his round of 16 tie against Spain’s Pablo Carreno Busta.

Djokovic will now face Alexander Zverev, who defeated 23rd seed Dusan Lajovic in straight sets, with the winner advancing to the semifinals. With the extent of Djokovic’s injury still a mystery, there’s no guarantee he will be fit to face the German, although many had similar thoughts ahead of his match against Raonic.

“If it was any other tournament, I would retire. I definitely wouldn’t be playing,” Djokovic said. “But it’s a Grand Slam. It matters a lot to me at this stage of my career. I have to accept the circumstances and the condition I’m in at the moment and that I’ll probably feel pain all of the way through.

“Against Sascha, there’s probably going to be more rallies, grueling rallies. It’s going to be demanding from my side, really from the back of the court. It’s in God’s hands where my condition goes from today to the first point against Sascha [but] if I feel 10%, I like my chances.”

If Djokovic has indeed torn his oblique, regardless of the grade of the injury, it’s going to be a case of management, as opposed to having it fully healed before the end of the tournament.

“Most of his time between suffering the original injury and his next round will be spent in recovery, getting treatment,” Bell said. “Given the demands of a Grand Slam tournament, balancing recovery while maintaining conditioning and readiness to play will be the challenge.”

Djokovic’s record on the blue courts of Melbourne Park is 76-5, and post-fourth-round is an even more impressive 24-3. Even at 75% healthy, Djokovic would likely still be favored to beat just about everyone left in his path to Slam No. 18.