Alejandro Villanueva said standing alone on the field for the national anthem before the Pittsburgh Steelers-Chicago Bears game was a mix-up and he is "embarrassed" for it.

Villanueva's appearance on the field, hand over his heart during the national anthem while the rest of his team-mates remained behind in the locker-room tunnel, was one of the most striking images on a day of unprecedented protests around the NFL.

A former US Army Ranger who served three tours in Afghanistan, Villanueva was hailed by many fans as a hero.

But Villanueva said his stance on the field resulted from a communication mistake, and he now regrets how he made his team-mates look.

"Every single time I see that picture of me standing by myself, I feel embarrassed,” Villanueva said, via the Pittsburgh Post-Gazette.

"Unfortunately, I threw [my team-mates] under the bus, unintentionally."

As Steelers quarterback Ben Roethlisberger explained the situation to reporters on Monday, Villanueva was supposed to stand up front with the team captains near the head of the tunnel during the anthem.

But the small area became congested with people running off the field, and Villanueva got separated from his team-mates.

"When we came out of the locker room into that tunnel, it was a very small area," Roethlisberger said.

"There was a flag or something coming off the field so there were a bunch of Bears fans, coming off the field holding that [and] going in front of us, so it kind of held us up."

Villanueva said when the anthem started, it was too late for him to leave the field. He says he takes full responsibility for getting separated from the team.

"I made coach [Mike] Tomlin look bad, and that is my fault and my fault only," he said. "I made my team-mates look bad, and that is my fault and my fault only."

Both Villanueva and Roethlisberger regretted the way the entire situation played out. Roethlisberger said the team will be on the field for the anthem before their next game Sunday in Baltimore.

"We as a team tried to figure it out, obviously we butchered it... I'm not going to pretend I have some kind of righteous voice," Villanueva said.