England forward Jadon Sancho was among a number of sports stars adding their voice to worldwide protests against racism on Sunday.
Protests have been held after George Floyd, an unarmed black man, died while being restrained by Minneapolis police.
Sancho unveiled a 'Justice for George Floyd' T-shirt after scoring for Borussia Dortmund against Paderborn.
Earlier, Marcus Thuram took a knee after scoring for Borussia Moenchengladbach.
Sancho, who scored a hat-trick as Dortmund thrashed Paderborn 6-1, was shown a yellow card for the gesture.
Sancho later wrote on Instagram: "Delighted to get my first career hat trick, a bittersweet moment personally as there are more important things going on in the world today that we must address and help make a change.
"We shouldn't fear speaking out for what's right, we have to come together as one & fight for justice. We are stronger together! #JusticeForGeorgeFloyd."
Floyd died in police custody on Monday after white officer Derek Chauvin kneeled on his neck for almost nine minutes to pin him down.
Chauvin has since been charged with his murder and sacked.
Marcus Thuram took a knee in tribute to George Floyd
American tennis player Serena Williams, a 23-time Grand Slam champion, shared a lengthy post on Instagram.
Underneath a video of a young black girl asking why she is treated differently to others because of her skin colour, a "heavy-hearted" Williams wrote that she was "lost for words".
Two-time Grand Slam champion Naomi Osaka wrote on Twitter: "Just because it isn't happening to you doesn't mean it isn't happening at all."
Teenager Coco Gauff, who had a fairytale run at Wimbledon in 2019, urged her Twitter followers to "demand justice for George Floyd".
The 16-year-old posted the faces of black Americans who died in recent years at the hands of authorities or white fellow citizens, asking: "Am I next?"
Coco Gauff posted this image on Instagram, with the caption: "When will it stop? When will we been seen as human and not a threat?"
Liverpool striker Rhian Brewster wrote a lengthy post on Twitter: "This is way deeper than just pointing out who's staying quiet and whose speaking up."
Brewster, who has previously spoken about the racist abuse he has suffered, continued: "For years and generations, we've been screaming out for change and to be heard, yet the pain continues.
"We don't want special privilege. A level playing field is all we have been crying for, forever.
"Hear us. #BlackLivesMatter."
Vanessa Bryant, the widow of basketball legend Kobe, shared an image of her husband wearing an 'I Can't Breathe' t-shirt.
"My husband wore this shirt years ago and yet here we are again," she wrote.
"Life is so fragile. Life is so unpredictable. Life is too short."
Formula 1 champion Lewis Hamilton criticised those in his industry for not speaking out.
"I'm one of the only people of colour and yet I stand alone," the Briton, 35, wrote on his Instagram story.
"I would have thought by now you would see why this happens and say something about it but you can't stand alongside us."