(CNN) -- World No. 1 Victoria Azarenka suffered a blow in the preparations to her Australian Open title defense on Friday, pulling out of a much-anticipated rematch with Serena Williams due to a toe problem.
The Belorussian was due to play her U.S. Open final conqueror in the semis of the Brisbane International, her first top-level warmup event for the season's opening grand slam -- which starts on January 14.
World No. 2 Maria Sharapova is also battling to be fit for Melbourne, having withdrawn before the beginning of the Brisbane tournament due to a collarbone problem.
"It's a right toe infection -- it's been there for about 10 days and it's been getting worse," Azarenka told reporters.
"I had to take action on it, which I did yesterday -- it was a minor surgery, I had to take something out of my toe. And unfortunately I didn't have enough time to recover to be able to play the semifinals today."
The 23-year-old won her first grand slam title in Melbourne last January before going on to top the rankings and become the WTA Tour's leading prize money winner for 2012.
"I had to make sure I could be fully recovered and ready for the Australian Open. It's a compromise I kind of had to take," she said.
"The doctor had told me I wouldn't be able to play for three, four days, but today I saw him in the morning and he said it was actually much better than he thought -- he expected a much worse outcome. So maybe two days and I can start slowly."
Williams, who last month also had toe surgery, will play Russia's Anastasia Pavlyuchenkova in Saturday's final.
"I had that toe problem just a couple of weeks ago and it's painful -- God, it's so painful. Doesn't sound painful, but it is. You can't walk with that. I hope she gets better fast," the American said.
"I'm definitely doing enough to prepare and be ready. I feel like even though I didn't play a match tonight I played some really good matches here."
Pavlyuchenkova ended the dream run of Lesia Tsurenko, a 116th-ranked Ukrainian who only made it into the main draw as a lucky loser from the qualifiers.
"What can I say about Serena? There's so much to say -- she's just a great champion," the world No. 36 said of the Olympic and Wimbledon titleholder.
Williams is seeking her 47th career title, already holding the record among active players -- her older sister Venus is second with 44.
"There's some chance, but with her power and the way she can serve, it will be difficult," Pavlyuchenkova said.
Meanwhile, defending champion Andy Murray moved into the semifinals of the Brisbane men's event with a 6-4 7-6 (7-3) win over Uzbekistan's Denis Istomin on Friday.
The world No. 3 will next play Japan's Kei Nishikori, who he beat in last year's Australian Open quarterfinals.
Fifth seed Nishikori earned a semi spot by beating Alexandr Dolgopolov, the 2012 Brisbane runnerup.
The other semifinal will be between 2006 Australian Open finalist Marcos Baghdatis of Cyprus and 21-year-old Bulgarian Grigor Dimitrov, who upset Austrian seventh seed Jurgen Melzer.
World No. 1 Novak Djokovic will play in Saturday's final of the Hopman Cup teams event after he and Serbian playing partner Ana Ivanovic whitewashed Germany 3-0 in Perth on Friday.
Djokovic thrashed veteran Tommy Haas 6-2 6-0 then former women's No. 1 Ivanovic -- whose injury in 2011 meant the pairing could not play in that year's final -- defeated Tatjana Malek 6-0 6-1 in just over half an hour.
They also won the mixed doubles to complete a third successive victory in Group A and set up a clash with Spain's Fernando Verdasco and Anabel Medina Garrigues, who won all three of their Group B matches.