Tennis - Pan Pacific Open Women's Singles Final match - Arena Tachikawa Tachihi, Tokyo, Japan - September 23, 2018. Naomi Osaka of Japan returns a ball to Karolina Pliskova of Czech Republic. REUTERS/Toru Hanai

(Reuters) - U.S. Open champion Naomi Osaka withdrew from the Wuhan Open in China on Sunday, hours after losing to former world number one Karolina Pliskova in the final of the Pan Pacific Open in Tokyo.

Wuhan Open organizers said on Twitter that Osaka had withdrawn due to a viral illness.

The Japanese world number seven was beaten 6-4 6-4 by Pliskova in Tokyo and said afterwards that she was suffering from fatigue.

The Wuhan Open, which began on Sunday and ends on Sept. 29, still boasts a strong field despite Osaka’s withdrawal, with the top five women’s players, including world number one Simona Halep, all taking part.