Four-time Grand Slam champion Naomi Osaka was knocked out of the first round of the WTA event in Rouen on Wednesday, losing 6-4, 6-2 to Italian Martina Trevisan.

The former world number one was making her first appearance on clay since the 2022 French Open, when she was knocked out in the opening round and Trevisan reached the last four.

Osaka, 26, returned to action in January after taking a 15-month break from the tour due to maternity leave.

On Saturday, Osaka she would like to play in the Paris Olympics but might need to go through an appeals process after failing to make a mandatory two appearances for Japan in the Billie Jean King Cup during the current Games cycle.

Osaka's world ranking has risen from 831 to 192 since her comeback, although she has not gone beyond the quarter-finals in seven tournaments.

In Rouen, Trevisan broke Osaka in the first game only for the former US and Australian Open champion to hit straight back.

Osaka converted just one of eight break chances in the opening set, which a resilient Trevisan won after nudging ahead in the ninth game.

She carried that momentum into the second set and broke a rusty Osaka again in the third and seventh games to claim victory, only her second in nine tour-level matches this year.

Trevisan will play Ukrainian third seed Anhelina Kalinina in the last 16.