The Japanese superstar made the announcement just hours before she was due to meet Australian qualifier Maddison Inglis on centre court in Melbourne.

"I've had to make the difficult decision to withdraw to address something my body needs attention for after my last match," said the 16th seed on Instagram.

"I was so excited to keep going and this run meant the most to me, so having to stop here breaks my heart. But I can't risk doing any further damage so I can get back on court."

The four-time major champion, who won the Australian Open in 2019 and 2021, said in later remarks to the media that it was an injury she had suffered from "a couple of times before".

"I thought I could push through it. I played my last match with some pain, and I thought maybe if I gave myself a break before my match today, I would be able to handle it.

"But I warmed up and it got a lot worse."

The 28-year-old mother of one said she needed to see a doctor for more tests.

"Obviously I think coming back from pregnancy, my body changed quite a lot. So this is something I have to be really cautious of," she said.

She also found herself caught up in controversy in round two, at the centre of a row with veteran Sorana Cirstea.

Cirstea took issue with Osaka shouting "come on" between the Romanian's first and second serves.

During her on-court interview, Osaka was dismissive of Cirstea, but later apologised for being "disrespectful".

Her actions drew rebukes from tennis greats Martina Navratilova and Lindsay Davenport, who said she had failed to keep to "basic etiquette" in not making noises between an opponent's serve.