Venus - who turned 19 on Thursday and is seeded No 6 - is also fighting off the bug, her father said.
Serena Williams, 17, was to have been the No 10 seed when the two-week tournament opened Monday. She will be replaced by the Russian Anna Kournikova, who was the highest ranked player not to be placed among the 16 seeds. Kournikova will now take Williams' place in the draw but will be called the 17th seed.
"She's has a terrible case of the flu," Serena's father Richard said in a statement released by the WTA Tour. "Serena wanted to go to Wimbledon and give it a try ... but the doctor said again it was better if she rested.
"Venus is a little sluggish because they hang out a lot together, but we're hoping she'll be all right." He said he did not expect Serena to travel to England.
The Williams sisters were seeded No 4 in doubles and have also pulled out with Venus not seeking a replacement. The sisters always play doubles together and did not want to break up the partnership.Reuse content