TOKYO, Japan (AFP) — Naomi Osaka's woes deepened when the struggling former world No. 1 pulled out of her home Pan Pacific Open in Tokyo complaining of abdominal pain.

The 24-year-old Japanese was set to play Brazil's Beatriz Haddad Maia in the second round later in the day but withdrew saying her "body won't let" her compete.

"It's an honor to be able to play at the Toray Pan Pacific Open in front of the amazing fans here in Japan," Osaka said in a statement released by organizers.

"This has and always will be a special tournament for me and I wish I could have stepped on court today, but my body won't let me."

"Thank you for all your support this week and I will see you next year," she added.

Osaka, a four-time Grand Slam winner, was looking to end a poor run of form in Tokyo, where she is the defending champion from the last time the tournament was played in 2019.

She has plummeted to 48 in the women's world rankings after a wretched run that saw her crash out in the first round of her previous three tournaments.

Osaka's first-round match in Tokyo against Australia's Daria Saville lasted just seven minutes before her opponent collapsed with an injured knee.

Saville retired from the match and was later found to have torn her anterior cruciate ligament.

Osaka admitted on Monday that she had gone through "more down than up" this year.

"This year has been not the best year for me but I've learned a lot about myself," she said, adding that she was "happy to be healthy."

"Life is ups and downs, and this year was more down than up, but overall I'm pretty happy with where I am now."