The balky knee has slowed the seven-time Grand Slam champion Williams for most of the second half of the season.
"I am very disappointed to announce that I will be unable to play in the season-ending WTA Championships and Fed Cup final," Williams said in a statement. "I have been getting treatment and therapy on my knee and have been making progress, but unfortunately must continue to keep weight off my knee for the short term and won't be ready to return to competition in 2010."
In addition to the WTA Championships in Doha this month, Williams will miss next month's Fed Cup final between the United States and Italy in San Diego.
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