MASON, Ohio -- Serena Williams has withdrawn from the Western & Southern Open, citing a lingering back injury.
The 23-time Grand Slam champion retired because of the same injury during Sunday's Rogers Cup final in Toronto against Bianca Andreescu, but Williams had been expected to open play in Cincinnati on Tuesday.
She made the announcement shortly before the start of her scheduled first-round match against Zarina Diyas on Tuesday night.
Williams, a two-time winner at the event, will be replaced by lucky loser Jessica Pegula.
"I am so sad to withdraw from the Western & Southern Open as it is truly one of the tournaments I most love to play," Williams said in a statement provided by the tournament. "I came to Mason on Sunday and have tried everything to be ready to play tonight, and was still hopeful after my practice this morning. But unfortunately my back is still not right and I know I should not take to the court.
"I really want to thank tournament director Andre Silva and the WTA for giving me every chance to play, and I also want to thank all the amazing fans here in the Cincinnati area for their support -- it means so much. I promise I'll do my best to be back here next year."
Williams is next expected to play in New York at the US Open, which begins Aug. 26 and where she is a six-time champion and the 2018 runner-up.