Serena Williams out of Dubai Championships

World number one Serena Williams has been forced to pull out of the Dubai Championships due to a lower back injury.

The American, who secured the top ranking last week in Qatar, was due to face Marion Bartoli on Wednesday, but the issue has forced her to retire from the competition.

Williams, who lost in the quarter-finals of the Australian Open last month, has suffered from the persistent injury in recent months, but it is not yet clear how long she will spend on the sidelines.

Second-ranked Victoria Azarenka was also forced to withdraw from the competition on Monday, citing a foot injury as the cause.