(CNN) -- Victoria Azarenka has been forced to withdraw from the Dubai Open for the second successive year after suffering an injured heel.
Azarenka, who surrendered the World No.1 spot Monday to Serena Williams, was hoping to build on her title win at the Qatar Open where she defeated the U.S. star.
The Belorussian would have regained the No.1 ranking had she won the tournament, but Williams is set to remain at the summit until the Indian Wells tournament next month.
"I'm very disappointed, but I have to listen to my body," Azarenka told reporters.
"The injury happened last week when I played a lot of tennis, so going on to a new tournament is just too much. The heel kept getting worse, and I needed to re-evaluate.
"Sometimes the schedule is just too difficult. Unfortunately you can't know when you plan it in November what will happen in February.
"I didn't want to continue taking painkillers because sometimes it's better to feel the pain. so that you can control the injury. Otherwise it can cause something which is much worse.
"This is just a warning that I have to take care of myself."
Azarenka, who has a 14-0 record this year, revealed that the physical demands of the schedule has become a growing concern since she won the Australian Open last month.
"I never realised before just how much it takes out of you," she said. "Physically and mentally it just drains you out - and then you realise."
Meanwhile, Williams, who is the oldest woman to ever hold top spot in the rankings, is the big favorite for the $2 million tournament.
And the 31-year-old says she's feeling in rude health going into the competition.
She told reporters: "I was really, really, really, really sick last week and physically I just wasn't at my best, considering I couldn't train, and I didn't practice.
"I practised only one or two days before playing because I had the ankle problems.
"But I didn't want to not show up and not play. So at least if I could show up and play my way into shape I would be able to compete and that's what I did.
"I feel so much better this week already. I feel like a completely different athlete, and a completely different person, compared with last week."