In a statement e-mailed to the AP by her agent, the younger Williams said Tuesday she "re-tore the tendon" in her right foot, which she originally injured by cutting it on glass at a restaurant shortly after winning Wimbledon in July. Williams had surgery in New York on Monday; she first had the foot repaired July 15.
Her announcement comes less than two weeks after Venus Williams said she won't play for the rest of the year because of a lingering injury to her left knee. Both sisters will miss the WTA Championships next week in Doha, Qatar, and the Fed Cup final between the United States and Italy next month at San Diego.
Serena hasn't played on tour since July 3, when she overwhelmed Vera Zvonareva 6-3, 6-2 to win her fourth Wimbledon championship and 13th Grand Slam singles title overall, the most among active women.
The American cut her right foot on glass at a restaurant while she was in Munich after her victory at the All England Club, but she went ahead and played in an exhibition match July 8 in Brussels against Kim Clijsters that drew a tennis-record crowd of more than 35,000. A week later, Serena had an operation on the foot in Los Angeles.
After withdrawing from the U.S. Open, she returned to practice in September, but then put off her comeback by pulling out of tournaments in Tokyo, Beijing and Linz, Austria.
On Oct. 10, in a posting on her official website, Serena said she "re-strained" her foot by overtraining and "likely" would be out of the year.
Her statement Tuesday said: "It is with deep frustration that I am withdrawing from the WTA Championships at Doha and the Fed Cup Final. Pushed by my desire to return to competition, I trained too hard too soon and re-tore the tendon in my foot. As a result, yesterday morning I had to have another procedure to repair it. I thank everyone for their continued support during this difficult time and look forward with strength and determination to getting back on the court."
Earlier this year, Serena missed all of February, March and April because of a left knee problem. So she closes 2010 having participated in only six singles tournaments, going 25-4 with two titles at the Australian Open and Wimbledon.
She lost the No. 1 ranking last week to Denmark's Caroline Wozniacki, who has yet to win a Grand Slam tournament.
Serena also went 18-1 with three doubles titles in 2010, all with Venus as her partner. In singles, Venus went 38-7 with two titles and is No. 4 in this week's WTA rankings, two spots behind Serena. Venus announced on Oct. 6 that she would be sidelined for the rest of this season because her knee injury.
In August, both Williams sisters told the U.S. Tennis Association they planned to play against Italy in the Nov. 6-7 Fed Cup final on an indoor hard court at the San Diego Sports Arena.
"It's unfortunate about Venus and Serena. The team was really looking forward to having them on the team," Fed Cup captain Mary Joe Fernandez said in a statement released by the USTA on Tuesday. "We wish them a speedy recovery. Our team is excited to be in final for second straight year and we will give it our all as usual and try to pull off another upset."
Neither Williams has competed for the U.S. Fed Cup team since 2007.
The rest of the U.S. roster includes 2009 U.S. Open quarterfinalist Melanie Oudin, Bethanie Mattek-Sands and leading doubles player Liezel Huber.
The United States hasn't won a Fed Cup title since 2000 and lost to Italy in last year's final.