ST. PETERSBURG, United States, (AFP) - World number one Serena Williams has withdrawn from next week's US$2.4 million (S$3.04 million) Qatar Open because of a back injury, the WTA Tour announced on Friday.
Williams, who lost to Victoria Azarenka in last year's Qatar Open final, suffered the injury at the Australian Open last month.
Serbian Ana Ivanovic upset Williams in the fourth round in Melbourne.
Williams, who won her opening tournament of the year at Brisbane by beating Azarenka in the final, is the reigning US and French Open champion.
The 17-time Grand Slam singles champion will try to move nearer Steffi Graf's Open-era record of 22 Slam singles crowns in May at the French Open.
Williams has entered next month's WTA Tour event at Indian Wells, a tournanment she and her elder sister Venus have boycotted since 2001 when she was fiercely booed as she played Kim Clijsters in the final.
Spectators were angry at the time after Venus had defaulted to Serena due to tendinitis just moments before they were scheduled to meet in the semi-finals.