Injured Kyrgios out of Australian Open

Nick Kyrgios's best chance to win the Australian Open may have come and gone after the shattered star was forced out of the Melbourne Park major with a knee injury.

"Going in as one of the favourites, it's brutal," Kyrgios said after joining the Open's alarming casualty list on Monday.

Kyrgios's long-time physio Will Maher said the 2022 Wimbledon runner-up had a cyst growing on his left meniscus and needed arthroscopy surgery.

While it's not a career-threatening setback, Kyrgios made the "sensible" decision to pull out to avoid suffering long-term damage.

But it was still one of the most agonising calls of his tumultuous career.

"It hasn't been easy at all," Kyrgios said.

"I'm devastated obviously. It's like my home tournament. I've had some great memories here. Obviously last year winning the title in doubles and playing the best tennis of my life probably.

"I've worked so hard, put myself in the position to (challenge for the title).

"I was ranked outside 100 a year ago. Now I've had the year I had last year and back inside the 20, being seeded at a grand slam, feeling as good as I'm feeling and playing the way I'm feeling.

"Yeah, I wanted to give myself a chance."

With world No.1 Carlos Alcaraz not competing, nine-times champion Novak Djokovic also under a fitness cloud, six-times winner Roger Federer retired and Kyrgios at the peak of his powers, 2023 may well have been the mercurial talent's greatest chance yet to win his home slam.

The 19th seed had been due to play Russian Roman Safiullin in the first round on Tuesday night but Maher said it was too risky to take the court.

"Unfortunately, during the last week or so Nick's experienced some discomfort in his knee," Maher said.

"He had routine MRI just to make sure everything was OK. There's a parameniscal cyst growing on his lateral meniscus, which is a result of a small tear in his lateral meniscus.

"It's not a significant injury in the sense that it's going to be career threatening or anything like that.

"It was even at that stage it was still worth persevering to see if we could do anything to get him back on court.

"And to Nick's credit, he did try everything to the point even last week he was having a procedure to drain the cyst and any amount of injections that he could try and get in his knee without causing long-term damage."

Kyrgios used a charity exhibition match against Djokovic last Friday night as a gauge if he could compete at the highest level.

"He didn't pull up great," Maher said.

"He still tried to give himself every chance in the following days to have subsequent training but it was clear that with each passing session that he was getting sorer and sorer."

The 27-year-old will return home to Canberra to have an arthroscopic procedure to clean up his knee, Maher said.

"And then from there, it's relatively straightforward recovery through February for him and very realistically back on the court for Indian Wells so it won't interrupt his year tremendously.

"The prognosis is good and he'll be fine."

Kyrgios's scratching is another hammer blow to the summer slam, which was already ravaged by superstar withdrawals and retirements.

Women's titleholder Ash Barty, seven-times champion Serena Williams, her sister Venus, dual winner Naomi Osaka, Alcaraz and Federer are all missing.

Australia's highest-ranked woman Ajla Tomljanovic also pulled out on Saturday with a knee injury.

But Kyrgios's absence is undoubtedly the biggest shocker yet for organisers.