Naomi Osaka pulled out of the semi-finals of the Western & Southern Open tennis tournament on Wednesday in protest at racial injustice.
Osaka, who has a Japanese mother and Haitian father and has been a vocal supporter of the "Black Lives Matter" movement, said in a social media post: "Before I am an athlete, I am a Black woman".
Her decision follows protests over the police shooting of Jacob Blake, a Black man, in the city of Kenosha, Wisconsin, on Sunday.
Earlier on Wednesday, the National Basketball Association postponed three playoff games after the Milwaukee Bucks boycotted Game 5 of their playoff series against Orlando Magic in protest over racial injustice.
In Osaka's statement, posted on Twitter, she said she was making the decision to move the conversation forward.
"As a Black woman I feel as though there are much more important matters at hand that need immediate attention, rather than watching me play tennis," the world number 10 wrote.
"I don't expect anything drastic to happen with me not playing, but if I can get a conversation started in a majority white sport I consider that a step in the right direction.
"Watching the continued genocide of Black people at the hand of the police is honestly making me sick to my stomach."
Osaka beat Anett Kontaveit 4-6 6-2 7-5 on Wednesday to reach the semi-finals, where the two-time Grand Slam champion was due to face Elise Mertens.
(Editing by Peter Rutherford)
