Serena WilliamsWorld No. 1 Serena Williams of the USA has pulled out of yet another tournament, the China Open in Beijing while she continues to recover from surgery on her right foot. The injury will keep her from competing at the Pan Pacific Open and China Open tournaments over the next two weeks.

At the beginning of the week, the 13-time Grand Slam champion revealed to fans on her website that she had stopped wearing a protective boot around her injured foot. “While I have continued to make progress in the recovery of my foot injury, unfortunately I am still not ready to compete at the upcoming Toray Pan Pacific Open in Tokyo and China Open in Beijing,” Williams said in a statement.

“These are both fantastic events with loyal fans that I hope to be able to compete in next season. In the meantime I am focused on my rehab program and remain optimistic to return to competition this season.”

According to the Sony Ericsson WTA Tour, in Serena’s absence from both Asian events, Caroline Wozniacki and Vera Zvonareva both have a mathematical chance of seizing the No.1 spot, but not until the week of the Beijing tournament (4-10 October). The 19-year-old Dane, runner-up at the US Open last year, will have three opportunities to become the first Dane to be ranked No.1 in the world: if she wins Beijing (regardless of her result in Tokyo), if she reaches the semi-finals or better in Tokyo and the final in Beijing, or, if she wins Tokyo and makes the quarter-finals or better in Beijing.

In the event that Wozniacki does not achieve either of the three scenarios, should Zvonareva win both titles, or reach the final in Tokyo and win the Beijing tournament, she will overtake Serena as the world No.1.

Maria Sharapova and Svetlana Kuznetsova are the defending champions in Tokyo and Beijing respectively.