(Tom Uhlman / AP)

Williams, who has won her last two tournaments as she prepares for the U.S. Open later this month, won a match Tuesday, but had swelling in her foot and decided to withdraw.

“I definitely don't want to overdo it,” Williams said, via Reuters. “My main goal right now is obviously to do well and nothing against Cincinnati or Toronto or the Stanfords that I played, but this is all preparation. Everyone is preparing for the U.S. Open. So I have to be smart and make sure it's not too much.”

Williams is carefully managing her return to tennis after about 10 months away from the game. After winning Wimbledon last July, she cut her foot, an injury that started a cascade of health problems that sidelined her until May. She twice had surgery on her foot, then battled through blood clots in her lung.

Williams described her injury today as “a bit of an aggravation because I think I’ve been pounding it a lot and playing a lot.”

It’s not the kind of injury, though, that should keep her from rocking the wedding of her friend Kim Kardashian and New Jersey Nets forward Kris Humphries on Saturday in Montecito, Calif., though. Don’t be silly.

“Now that I have the time, I probably will [attend]. I hadn’t thought about it.”