Former World No. 1 Venus Williams withdrew from next week's WTA Qatar Open, citing a lower back injury.
The 32-year-old American, who was ousted by Maria Sharapova in the third round of last month's Australian Open, has been nagged by the injury since her loss in Melbourne.
Williams, ranked 23rd, pulled out of the WTA Paris Open and this week's US Fed Cup quarter-final tie at Italy because of the back injury.
Williams is a seven-time Grand Slam singles champion whose most recent major title came in 2008 at Wimbledon, where she is a five-time champion.
In 2011, she was diagnosed with Sjogren's syndrome, an auto-immune disease that can cause fatigue.