Williams has been out of action on the WTA Tour since downing Russian Vera Zvonareva July 3 to capture her fourth career Wimbledon title. She played an exhibition match four days later in Brussels but shortly thereafter injured her foot by stepping on broken glass at a restaurant.
The 29-year-old had surgery to repair the damage but on Tuesday said she had "re-torn" the tendon and underwent additional surgery Monday in New York.
"It is with deep frustration that I am withdrawing from the WTA Championships at Doha and the Fed Cup final," Williams said on her Web site. "Pushed by my desire to return to competition, I trained too hard too soon and re-tore the tendon in my foot."
A 13-time major champion, Williams lost her No. 1 ranking to Caroline Wozniacki of Denmark last week.
Her older sister Venus also ended her 2010 season early due to a knee injury, meaning neither of the American superstars will be available for the United States in the Fed Cup against reigning champion Italy.