Azarenka, the only unbeaten leading player on the tour this year, beat Williams in three sets in the final of the Qatar Open on Sunday, but had been playing part of the tournament with painkillers.
“I’m very disappointed, but I have to listen to my body,” said the Belarussian who lost the World No 1 spot on Monday to Williams despite her triumph the day before.
Azarenka could have regained the summit this week by winning the Dubai Open.
Williams is now likely to remain world number one at least until the Indian Wells tournament next month.
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