WASHINGTON — Naomi Osaka and coach Patrick Mouratoglou are done working together after less than a year, the four-time Grand Slam champion announced Sunday on social media.

“Merci Patrick,” Osaka began her post, with a photo of her hitting a practice serve while he stands nearby. “It was such a great experience learning from you. Wishing you nothing but the best. You are one of the coolest people I’ve ever met and I’m sure I’ll see you around.”

The news comes three days after Osaka lost her second match at the DC Open and just before she begins competing in Toronto. The US Open, the year’s last major tournament and an event Osaka won twice, begins in New York on Aug. 24.

Osaka hired Mouratoglou — who was the longtime coach of Serena Williams — when she fired Wim Fissette shortly after her second-round exit at last year’s US Open.

Osaka, a former No. 1, is currently ranked 51st and has a 21-11 record this season.

She hasn’t been past the third round at a Grand Slam tournament since winning the 2021 Australian Open.