Former No.1 Osaka splits with Belgian coach Fissette

"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.