Wimbledon champion Serena Williams said a right elbow injury forced her to pull out of the Swedish Open on Thursday.
Williams said she felt pain in the elbow in the first game of her first-round match on Wednesday, four days after winning her sixth Wimbledon championship and fourth successive Grand Slam title, but went on to roll Belgian qualifier Yasline Bonaventure 6-2, 6-1.
"I was having some pain in my elbow, and I felt a little bit in my match," she said in an interview with tournament organizers. "But this morning it really exploded (in practice) ... I really couldn't hit serves."
Appearing downhearted, the 2013 Swedish Open champion said she wanted to do what was best for her body, and made the right decision, despite it being a "really, really difficult decision."
Williams told spectators on court that she was sad to withdraw, and looked forward to playing again at Bastad.
"I always enjoy my time here in Bastad. I have such a great time. My fans here are really amazing, I love all you guys," she said to resounding applause.
It was unclear how bad was the injury, and how long she would be sidelined.
Tournament spokesman Marcus Duner said they were "obviously sad when the world's No. 1 can't continue to play."