The executive director of football's anti-discrimination Fare Network has criticised the referee who showed Jadon Sancho a yellow card for taking his shirt off to display a handwritten message which read: "Justice For George Floyd" after scoring for Borussia Dortmund against Paderborn.

Floyd, a black man, was filmed gasping for breath on Monday in Minneapolis while being pressed under the knee of a white police officer for several minutes. Floyd's death has sparked days of protests across the U.S.

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Four players this weekend in German football took a stand in support of the protesters -- Schalke's United States international Weston McKennie, Borussia Monchengladbach's Marcus Thuram and Sancho's Dortmund teammate Achraf Hakimi, making their point in the first major football league to resume during the coronavirus pandemic.

"The booking of Jadon Sancho, or any other player, for making a statement in support of a man who has been unjustly killed is the wrong decision," Piara Powar told The Associated Press. "This is not a party-political cause, or an issue that poses a threat to football but an expression of concern and solidarity from minority players."

McKennie donned an armband which read: "Justice for George Floyd," while Thuram went to one knee after scoring the first of his two goals in Gladbach's 4-1 victory over Union Berlin.

Hakimi revealed his own yellow "Justice for George Floyd" T-shirt when he netted Dortmund's fourth goal against Paderborn. The Moroccan was not booked.

The German FA have said they will investigate the players over the messages. However, in a case in 2014, then Cologne player Anthony Ujah -- who paid tribute to Eric Garner following his killing -- was only issued a warning.

"The DFB control body will attend to this issue in the coming days and scrutinise the circumstances of the case," a statement from the German FA read.

"Denying high-profile athletes an opportunity to express concern on big issues is neither correct nor can it be controlled in the post-Kaepernick era," Powar added.

San Francisco 49ers quarterback Colin Kaepernick took a knee during the national anthem in 2016 in silent protest of police brutality and racism that kicked off a period of pregame activism in the NFL.

ESPN's Germany correspondent Stephan Uersfeld contributed to this report