LOS ANGELES -- Venus Williams withdrew from the U.S. Open on Friday because of a stomach muscle injury, leaving the year's final Grand Slam tournament without both Williams sisters.
The tournament begins Monday in New York, where Williams has been practicing.
Serena withdrew after having left knee surgery Aug. 1 and will be out six-to-eight weeks.
Neither sister has played a match since Serena beat Venus in the Wimbledon final on July 5, when Venus was hampered by leg and stomach muscle injuries.
Since Wimbledon, Venus has spent time rehabilitating and receiving treatment while curtailing her physical activities in the hope that she would be ready to play in the Open.
"I kept thinking I would be able to compete," she said in a statement issued by her Los Angeles-based spokeswoman. "Unfortunately, it just wasn't meant to be. So, with regret, I have to pull out of this tournament and continue my recovery. I'm looking forward to playing again in the fall."
The world's fifth-ranked player, Venus has lost to Serena in the final of five of the past six majors, a streak that began at the 2002 French Open and extended to Wimbledon last month.
The only time the sisters didn't meet in a major final during that stretch was this year's French Open, when Serena lost to eventual champion Justine Henin-Hardenne in the semifinals.
Venus has a 26-5 match record this year, with one tournament victory.
Venus won the U.S. Open in 2000 and '01, the same years she was Wimbledon champion. She lost to Serena in last year's final.
Venus' stomach muscle injury first occurred earlier this year during a tournament in Warsaw, Poland. She withdrew from events leading up to the French Open in May, but played at Roland Garros, where she lost in the fourth round to Vera Zvonareva.
Then she lost the three-set Wimbledon final to her younger sister.
"Obviously the tour is very disappointed that neither Venus nor Serena is going to play in this year's U.S. Open," WTA Tour spokesman Darrell Fry said.
"But from our perspective, Venus and Serena's health comes first and we want both of them to take as much time as they need to recover from their injuries so they can get back to the tour and play as long as they want to play."
On Aug. 11, Kim Clijsters of Belgium overtook Serena for the world's No. 1 ranking. Clijsters is seeded No. 1 for the Open, and countrywoman Henin-Hardenne is seeded No. 2.
American Lindsay Davenport, the '98 Open champion, is the third seed.
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