The Broncos issued a statement that read, "While we encourage members of our organization to stand during the National Anthem, we understand and respect it being a personal decision."
A smattering of players around the league have said they will join in protest during the national anthem this weekend.
Marshall, who will turn 27 on Saturday, attended the University of Nevada with Kaepernick.
"I support Colin. I support 'Kaep.' I understand where he's coming from," Marshall told the Colorado Springs Gazette last month. "I definitely see what he's saying. I support him on that. I'm not mad at him for that. Some people are bashing him on the Internet, but I'm not bashing him at all. I support him."