Villanueva, a retired Army Ranger and veteran of combat in Afghanistan, said he received numerous texts from other veterans before the game imploring him to salute the anthem. He also noted the game was played at Chicago's Soldier Field, which is named to honor military veterans.
Villanueva confirmed statements made by Roethlisberger and defensive lineman Cam Heyward earlier in the day that they wanted to stand with him to support him but they were blocked by people going through the tunnel until the anthem began.
He said he had no doubt that if his teammates had known his intentions, they all would have stood with him, even those who were inclined to kneel or sit during the anthem.
"When everyone sees an image of me by myself, everybody thinks the team and the Steelers are not behind me, and that's absolutely wrong," he said. "It's quite the opposite."
Villanueva apologized to his teammates, head coach Mike Tomlin and the franchise, saying he felt "embarrassed" by photos showing him standing alone and appearing to break the image of unity the team wanted to project.