Novak Djokovic's quest for a 10th Australian Open crown could be in jeopardy due to a hamstring injury that has kept the 21-times Grand Slam winner away from practice sessions as he races to recover in time to play Grigor Dimitrov in the third round.

The injury has clearly taken its toll on the 35-year-old Serbian, who dropped a set in the second round.

With Rafa Nadal having already made a premature exit due to injury, losing Djokovic in the first week would not only open up the draw but rob fans of the possibility to watch the two most successful men's players with a combined haul of 43 Grand Slam titles

"My situation with my injury is not ideal," said Djokovic, who took a medical timeout during his four-set win over French qualifier Enzo Couacaud.

"I am not practicing basically on the days between (matches) because I'm trying to give myself more time possible for my leg to be in somewhat of an 'ideal' state for performance on a high level.

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"There's two choices: leave it or keep going. So I'm going to keep going. I'm going to try to play and compete with, of course, a great player Dimitrov."

This is not the first time Djokovic has soldiered on through an injury having suffered a painful abdominal muscle tear in his 2021 title run, but the former champion admitted things are different now.

"I don't know how my body's going to react. I hope for the best," he added.

With Rafa Nadal having already made a premature exit due to injury, losing Djokovic in the first week would not only open up the draw but rob fans of the possibility to watch the two most successful men's players with a combined haul of 43 Grand Slam titles.

But one player who has defied belief in advancing to the third round is three-times Grand Slam champion Andy Murray.

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The Briton has already spent over 10-1/2 hours on court after two marathon five-setters in Melbourne, with his second round win over Thanasi Kokkinakis wrapping up at 4:05 am local time.

Murray blasted the organizers after the late-night finish and they have duly handed the 35-year-old a 7 pm start when he takes on Spaniard Roberto Bautista Agut.

"You play in cold conditions, at that time of the day, with balls like that, you're going to get long rallies, long points," he said after the match which started at 10 pm.

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Women's fifth seed Aryna Sabalenka has yet to lose a match in 2023 after winning the Adelaide International 1 warmup event and resumes her hunt for a first Grand Slam title with a third-round match against Elise Mertens.

Belinda Bencic, who won the second Adelaide tournament, has also emerged as one of the top contenders in Melbourne and she is up against Italy's Camila Giorgi while fourth seed Caroline Garcia faces Laura Siegemund.