Kaepernick refused to stand for the anthem during San Francisco's preseason games, explaining it was to protest racial oppression and police brutality in the United States.
It opened a wide debate and put the microscope on a pregame tradition that has, for decades, been routine.
Marshall was standing with his hand over his heart during the anthem before a preseason game on Aug. 20.
He made no mention of his plans for Thursday's opener but shortly after the large American flag was unfurled, the fifth-year linebacker out of Nevada went to the end of a long row of Broncos and took a knee.
After the game, Marshall said he will continue to refuse to stand at the beginning of games.
“I’m not against the military, I’m not against the police or America. I’m just against social injustice,” Marshall said.