Williams won the Pan Pacific Open in Tokyo in 2001 and '02 but hasn't played in Asia since 2005.
"I'm disappointed to have to withdraw from the Pan Pacific Open, which I was very much looking forward to playing this year," Williams said. "Unfortunately, with the number of matches I have played throughout the summer, I need more time to properly recover."
Williams is 67-4 this year with nine tournament titles, including the French Open and the U.S. Open.
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