The 24-year-old Japanese was going to play Brazil‘s Beatriz Haddad Maia in the second round later in the day, but withdrew, saying her “body won’t allow” her to compete.
“It’s an honor to be able to play at the Toray Pan Pacific Open for the amazing fans here in JapanOsaka said in a statement from the organizers.
“This is and will always be a special tournament for me and I wish I could have stepped out on the track today, but my body won’t allow it.”
“Thank you for all your support this week and I’ll see you next year,” she added.
Osaka, a quadruple Grand Slam winner, wanted to put an end to poor form in Tokyo, where she has been the defending champion since the tournament was last played in 2019.
She has dropped to 48th in the women’s world ranking after a miserable run that saw her crash 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 dropped out of the race and was later found to have torn her anterior cruciate ligament.
Osaka admitted on Monday that she had gone “more down than up” this year.
“This year wasn’t the best year for me, but I learned a lot about myself,” she said, adding that she was “lucky to be healthy.”
“Life has ups and downs, and this year was more down than up, but overall I’m pretty happy with where I am now.”
Osaka has been out of the top 10 all year, having endured first-round defeats at both the French and US Opens.
She withdrew from Wimbledon with an Achilles tendon injury after initially considering skipping the tournament because no ranking points would be awarded.
Osaka has previously spoken of struggles with her mental health.
Her withdrawal from the Pan Pacific Open was just the final blow to the tournament, which saw several big names knocked out in the opening rounds.
Top-class Paula Badosa of Spain and runner-up Caroline Garcia of France were eliminated in their opening matches, along with Wimbledon champion Elena Rybakina.
Number six seed Karolina Pliskova lost 6-3, 6-4 to Croatian Petra Martic in the second round on Thursday and became the last victim.