Naomi Osaka said she was encouraged by her progress on clay ahead of the French Open, as the four-time Grand Slam winner eyes an elusive trophy on tennis' slowest surface since returning from a 15-month maternity break.

Former world No. 1 Osaka, who returned to action in January, has had major success on hard courts thanks to her explosive baseline game, but the 26-year-old from has usually struggled on clay.

Osaka, who is now ranked 134th after her long break, has never reached a final on the surface and has yet to advance beyond the third round at Roland Garros.