(Reuters) - Japanese world number one Naomi Osaka retired from her Cincinnati Masters quarter-final with an apparent knee injury on Friday.
Osaka, who was playing American Sofia Kenin, sought treatment on the knee in the third set, then pulled out. Kenin was ahead 6-4 1-6 2-0 at the time.
The injury comes less than two weeks before the start of the U.S. Open, where Osaka is the defending champion.
Reporting by Gene Cherry in Raleigh, North Carolina, editing by Pritha Sarkar