The former world number one has been sidelined since she retired from her last-16 match at the China Open against eventual champion Coco Gauff at the start of the month.
She then pulled out of this week's Japan Open in Osaka.
The 27-year-old was set to compete at the Pan Pacific Open as a wild card but organisers said she would be "absent because of a lower back injury".
Osaka's appearance at the China Open was her first tournament under Patrick Mouratoglou, the Frenchman best known for being the long-time former coach of Serena Williams.
She has struggled for consistency since returning to tennis in January after the birth of her daughter Shai in July 2023. Her best results since becoming a parent have been two quarter-final appearances.
China's Olympic champion Zheng Qinwen - ranked number seven in the world - is the top-ranked player at the Pan Pacific Open.
Russia's Daria Kasatkina and Brazil's Beatriz Haddad Maia are also set to compete.
