He was coming off a fine run at the Western & Southern Open in Cincinnati, where he defeated Rafael Nadal in the quarterfinals and later advanced to the final before losing to Grigor Dimitrov.

■ CoCo Vandeweghe , who reached the Australian Open semifinals and the Wimbledon quarterfinals this year, defeated her fellow American Alison Riske, 2-6, 6-3, 6-4.

Further complicating the scene, Bouchard is the plaintiff in an active lawsuit against the U.S.T.A., seeking damages for a concussion she sustained at the tournament in 2015, which she said was caused by a slippery floor.

From February through the fourth round of the French Open, she compiled a 31-8 record, which included a title in St. Petersburg; finals in Acapulco, Stuttgart and Madrid; and a semifinal in Indian Wells.

But after an electrifying win in the fourth round of the French Open over the defending champion Garbiñe Muguruza, Mladenovic has stalled, going 7-10 and losing her last five matches, all in straight sets.