Jelena Ostapenko, the 2017 French Open champion, pulled out of the US Open, citing a change of schedule.
She is the latest woman with a Grand Slam title or high ranking to withdraw from the tournament that begins next week amid the coronavirus pandemic.
Six of the top eight women in the WTA rankings already were out, including No. 1 Ash Barty, the reigning champion at Roland Garros, and No. 6 Bianca Andreescu, the 2019 winner at Flushing Meadows.
Also pulling out Monday was Carla Suarez Navarro, who was fined $40,000 of her $58,000 prize money at the US Open last year for what was deemed a lack of effort after she retired from her first-round match with a lower-back injury.
With the two withdrawals, Kurumi Nara and Whitney Osuigwe were able to get into the main draw. A wild-card invitation awarded to Osuigwe was transferred to 16-year-old Californian Katrina Scott by the US Tennis Association.