Victoria Azarenka has pulled out of this week's Dubai Duty Free Championships because of a bone bruise in her foot.
Azarenka suffered the injury last week as she stormed to victory in the Qatar Open, where she beat Serena Williams in the final.
"I'm very disappointed, but I have to listen to my body," said Azarenka.
Although Williams was beaten in that match she earned enough points to return to No 1 in the world rankings, becoming the oldest player to hit that particular summit.
Azarenka's withdrawal ensures Williams will stay in that position for another week at least.
The 15-time Grand Slam winner last held the position in October 2010 before a serious foot injury that saw her drop to as low as 175th.