Colin Kaepernick knelt during the singing of the national anthem on Thursday.
Teammate Eric Reid, who was not in uniform, joined him in taking a knee just before the anthem began as boos rained down from the crowd. Reid has been outspoken about police brutality in the wake of the shooting death of Alton Sterling in that city and the impact it has had on him.
On Sunday, Kaepernick vowed to continue his protest during the national anthem until "significant change" is made regarding racial oppression in the United States.
Kaepernick sat on a cooler away from the team in the previous games.