Naomi Osaka [Source: AP]

Naomi Osaka has parted ways with coach Wim Fissette after four years together across two stints, the 26-year-old has announced.

The former world No.1 won two of her four grand slam titles under the guidance of the Belgian, but is currently 75th in the rankings having returned to the Tour nine months ago after a lengthy maternity break.

“Four years, two slams and a whole lot of memories,” Osaka wrote in an Instagram post.

“Thanks Wim for being a great coach and an even greater person. Wishing you all the best.”

Of the 16 tournaments Osaka has played this season, she has made the quarter-finals in only two – Doha and ‘s-Hertogenbosch – and the Japanese player has also failed to go past the second round in each of the four grand slams.