Naomi Osaka is nursing a knee injury just days before the first round of play in the US Open.
According to CNN, Osaka was forced to retire from the Cincinnati Masters on Friday due to her injury.
Osaka, who is the first player from Japan to win a major, quit in the third set of her quarterfinal match against American Sofia Kenin.
"My pain tolerance is really high, that's usually why I play through things that apparently I shouldn't".
In September 2018, Osaka won her first grand slam title, beating Serena Williams in a controversial US Open final.
This year's US Open competition begins Monday, August 26 and runs through Sunday, September 8th.