Serena Williams, the winner of 22 Grand Slam singles titles, has taken to Facebook to express her unease following the recent spate of black deaths at the hands of US police officers.
The post was prompted by the flurry of emotions she felt after seeing a police officer on the side of the road as her black nephew drove her to meetings.
She said the sighting caused her to quickly check "to see if he was obliging by the speed limit".
She then said, "I remembered that horrible video of the woman in the car when a cop shot her boyfriend", in relation to footage released by the family of a black man fatally shot by police in Charlotte.
"I am a total believer that not 'everyone' is bad It (sic) is just the ones that are ignorant, afraid, uneducated, and insensitive that is affecting millions and millions of lives," she continued.
"Why did I have to think about this in 2016? Have we not gone through enough, opened so many doors, impacted billions of lives? But I realized we must stride on- for it's not how far we have come but how much further still we have to go."
Williams said the incident in Charlotte made her question the safety of her nephew and ask: "What if I have a son and what about my daughters?".
She closed the post with a quote from prominent black activist Martin Luther King, which read: "There comes a time when silence is betrayal."
The post received mainly favorable responses, with one person commenting: "It is a sad reality for black people that anxiety does go up when a police car is seen - knowing that even if you comply - you can end up dead."
