Australian Open champion Caroline Wozniacki has withdrawn from the Citi Open because of an injured right leg.
The world No.2 was scheduled to play Ukrainian qualifier Anhelina Kalinina and her place in the draw will be filled by Belgian lucky loser Ysaline Bonaventure.
After practicing on-site on Monday, Wozniacki said her leg is "just something that has been nagging a little bit but hopefully it'll be fine."
Wozniacki hasn't played a match since losing in the second round at Wimbledon on July 4.
She has less than a month to prepare for the US Open, which starts August 27.
The hard-court WTA tournament also lost its defending champion Ekaterina Makarova.
The fourth-seeded Russian lost in the first round to Ana Bogdan 7-6 (7-2) 6-3.
There was no such trouble for reigning US Open champion Sloane Stephens.
The American second seed defeated countrywoman Bethanie Mattek-Sands 7-5 6-4 to set up a meeting with German Andrea Petkovic.
Stephens converted all four break points she earned and saved seven of the nine she faced.
Japanese third seed Naomi Osaka beat Bernarda Pera 6-2 7-6 (7-4) while seventh-seeded Croatian Donna Vekic defeated Caroline Dolehide 6-3 6-4.
Other winners on Tuesday were eighth-seeded Yulia Putintseva and Nao Hibino.
