Injury blow for Serena
New world number one Serena Williams has been forced to withdraw from this week's Dubai Tennis Championships due to injury.
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Williams was among the favourites for the title after replacing Victoria Azarenka at the top of the world rankings on Monday - but has confirmed her withdrawal due to a lower back problem.
"We were looking forward to seeing Serena play, and are disappointed that this injury has ruled her out," said tournament director Salah Tahlak.
"We wish her a speedy recovery and look forward to hopefully seeing her back in Dubai next year."
Williams had been due to face France's Marion Bartoli in the second round. Her withdrawal is a further blow for the tournament organisers after top seed Azarenka was also forced to pull out through injury.
Azarenka took her tally of career titles to 16 with victory over Williams in the Qatar Open final at the weekend, but that was not enough to ensure she could deprive the American of top spot when the new list was published on Monday.
Azarenka, who is unbeaten in 2013, withdrew with a foot problem suffered on her way to victory in Qatar last week.
Defending champion Agnieszka Radwanska is still fit and firing in Dubai and with Williams and Azarenka on the sidelines, the third seed is very much the firm favourite to retain her title this weekend.
The Pole booked her place in the quarter-finals but not before being forced to come from a break down in both sets as she saw off 18-year-old Yulia Putintseva of Kazakhstan 7-5 6-3.
Roberta Vinci of Italy is also safely into the last eight after seeing off fourth seed Angelique Kerber 7-5 6-1, while sixth-seeded Czech Petra Kvitova was made to fight hard for a 7-5 7-6 (7/1) win over former world number one Ana Ivanovic of Serbia.
Australia's Samantha Stosur, the seventh seed, was a 6-4 6-0 winner over Hsieh Su-Wei of Chinese Taipei, while eighth-seeded Caroline Wozniacki of Denmark swatted aside China's Zheng Jie 6-0 6-1 and Russia's Nadia Petrova was similarly ruthless as she ousted Spain's Carla Suarez Navarro 6-1 6-0.
In the late match, fifth seed Sara Errani of Italy had little trouble overcoming Romania's Sorana Cirstea, winning 6-4 6-4 to set up a last-eight meeting with Petrova.