Naomi Osaka Withdraws From Tennis Tourney Due To Abdominal Injury

Naomi Osaka announced she's pulling out of the semi-finals of an Australian Open warm-up tournament after she says her body went into "shock" from playing hard tennis ... after she took months off to focus on herself.

Now, the Australian Open -- already possibly without superstar Novak Djokovic -- could also be without one of women's tennis' biggest stars, Osaka.

Naomi, clearly bummed, announced she was withdrawing from the Melbourne Summer Set over an ab injury.

“I had a lot of fun playing here in Melbourne,” Osaka said in an official statement. “Unfortunately I have an abdominal injury which I need to rest and prepare for the Australian Open.”

Osaka expanded on the injury on social media, tweeting her body "got a shock from playing back to back intense matches after the break she took" ... forcing the former No.1 ranked women's tennis player to pull out at the last minute.

As we previously reported, Naomi returned to the tennis court in November ... after stepping away from the game to focus on herself following an emotional loss at the U.S. Open in September.

Osaka -- a four-time Grand Slam singles champion -- has been outspoken about her struggles with mental health in the past, infamously boycotting the media at the French Open.

And now, 24-year-old Osaka -- who was scheduled to play Veronika Kudermetova of Russia -- is sidelined once again ... as she tries to rehab her way back to competition.