Former world number one Venus Williams said on Friday that she has pulled out of February's US Fed Cup quarter-final tie against Italy and next week's WTA Paris Open because of a back injury.
Williams, ranked 26th, lost to reigning French Open champion Maria Sharapova last week in the third round of the Australian Open. She and sister Serena were ousted in the Australian Open women's doubles quarter-finals.
Just last week, Williams had said she was keen to play for the Americans in their tie at Rimini, Italy.
Williams, 32, 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.