Serena Williams has undergone surgery on both big toes, raising question marks about her fitness for next month's Australian Open.
The American, who dominated the second half of the 2012 season, has withdrawn from a scheduled exhibition match in Thailand at the end of this month following last week's "minor procedure".
Williams said: "I am being advised by my doctors to take more time to heal following a minor procedure I needed to address my ongoing foot issues."
A doctor's letter said Williams "was treated for a chronic foot disorder which involved minor procedures on both of her great toes."
The Wimbledon and US Open champion had been due to face Victoria Azarenka in Hua Hin on December 29 but that will not now happen. Li Na has been drafted in to replace her.
Williams' next scheduled appearance is at the Brisbane International, which begins on December 30.
The Australian Open, a tournament Williams has won five times, begins on January 14.