Playing in her first WTA final for three years, against Denmark's Clara Tauson, the four-time Grand Slam champion called for the physio after taking the opening set 6-4 and pulled out shortly afterwards.
Osaka's sudden withdrawal from the Australian Open warm-up event came as a shock after playing with no apparent problem in the 35-minute opening set, unleashing some powerful groundstrokes to break her opponent in the third and fifth games.
At the changeover, the 27-year-old stood and performed a series of stretches during a medical timeout.
After consulting with the trainer she shook the hand of Tauson, who picked up a third career title and her first since 2021.
Osaka didn't divulge details of what forced her withdrawal in a short courtside interview.
However, in a statement, the WTA said she retired "due to an abdominal injury".
"I just want to thank everyone for welcoming me to such a beautiful city and I had a lot of fun playing here and I'm really sorry about how it ended," Osaka said.
"I hope you did enjoy the tennis that we did play and I'm just really grateful to be here."
It was an anti-climactic finish to the week for Osaka, who was chasing her first title in four years since winning the 2021 Australian Open.
Her most recent final appearance was at the Miami Open the following year, before taking a 15-month break and giving birth to her first child midway through 2023.
She returned to tennis 12 months ago and has climbed to 57th in the world rankings.
Osaka arrived in Auckland professing her "deep love" of tennis was returning and voiced confidence about the possibility of a strong campaign at the year's first Grand Slam, starting in Melbourne on Sunday.
She appeared to find her rhythm as the Auckland tournament progressed, sweeping past four lower-ranked opponents.
Fifth seed Tauson conceded she had been outplayed in their lone set.
"I felt like today she was picking up an even higher level so I'm super sad about the way it ended," the 50th-ranked Tauson said.
"She's right to put her health first, always.
"But it's the worst final I've ever played emotionally because I can't feel happy and I'm just sad about what happened.
"Of course when I process this, I'm going to be super-happy about my week."
