(Reuters) – LeBron James was among a number of high-profile athletes who took to social media to speak out on the death of an unarmed black man seen in a video lying face down in the street while a white police officer knelt on his neck for several minutes.

Four Minneapolis police officers were fired on Tuesday over Monday’s incident in which a handcuffed George Floyd can be heard repeatedly moaning and gasping while he pleads, “Please, I can’t breathe, please, man.”

James, a four-time NBA Most Valuable Player, weighed in on Instagram late on Tuesday with a post that referred to Colin Kaepernick, the former NFL quarterback who famously kneeled during the U.S. national anthem to protest against racial injustice.

The post includes a photo of the officer pinning his knee on Floyd’s neck alongside a photo of Kaepernick kneeling during the national anthem while a member of the San Francisco 49ers.

Others in the sports world voiced their outrage over the incident that is likely to add fuel to the “Black Lives Matter” movement spawned by a series of U.S. police killings of unarmed black men.