Former world No. 1 Naomi Osaka announced the end of her working relationship with Belgian coach Wim Fissette following a poor run of results on Friday.

Japan's Osaka Naomi reacts during her women's singles third round defeat to Marketa Vondrousova of the Czech Republic at Tokyo 2020, July 27, 2021. (Xinhua/Dai Tianfang)

The Japanese tennis star revealed the news on Instagram, recalling their time together by saying, "4 years, 2 Slams and a whole lot of memories. Thanks Wim for being a great coach and an even greater person. Wishing you all the best."

The announcement came eight months into Osaka's return to the WTA Tour, which began at the Brisbane International in January.

Fissette first coached Osaka from 2019 to 2022 summer, while Osaka won the 2020 US Open and 2021 Australian Open titles.

Fissette rejoined Osaka's team ahead of her comeback from maternity leave last year after he shocked Chinese rising star Zheng Qinwen by abruptly ending their partnership.

Despite a refreshed, optimistic outlook on her career, Osaka has struggled to regain her top form since her return. The former world No. 1 did not pass the second round in any of the four Grand Slam tournaments in 2024.

With only two quarterfinal appearances in 16 tournaments this season, Osaka's ranking dropped to 75th in the world.