As part of a wave of protests throughout the NFL in the wake of President Donald Trump's NFL-related comments, most of the Steelers were not on the field for the playing of the national anthem before their game against the Bears on Sunday. The lone Steeler on the field for the anthem was offensive tackle Alejandro Villanueva, an Army veteran who served three tours of duty in Afghanistan.

MORE: Roethlisberger regrets anthem absence | Villanueva 'embarrassed' for standing alone

Before the game, Steelers coach Mike Tomlin told CBS his team would remain in the locker room for the playing of the Star-Spangled Banner.

Steelers head coach Mike Tomlin reveals to @JamieErdahl that the team will not be participating in today's national anthem. pic.twitter.com/5zihPWQsMv — NFLonCBS (@NFLonCBS) September 24, 2017

"These are very divisive times for our country," Tomlin said. "For us, as a football team, it's about us remaining solid. We are not gonna be divided by anything said by anyone. That's the thing that I posted to our guys. I said, 'If you feel the need to do anything, I'm going to be supportive of that. As Americans, you have that right.' But whatever we do, we're gonna do 100 percent, we're gonna do together. We're not gonna let divisive times or divisive individuals affect our agenda. This collection of men, we're chasing something here in 2017, and we're not gonna play politics with football players, with football coaches.

"We're not participating in the anthem today. Not to be disrespectful to the anthem, to remove ourselves from the circumstance. People shouldn't have to choose. If a guy wants to go about his normal business and participate in the anthem, he shouldn't be forced to choose sides. If a guy feels the need to do something, he shouldn't be separated from his teammate who chooses not to. So we're not participating today. That's our decision. We're gonna be 100 percent. We came here to play a football game. That's our intentions, and we're gonna play and play to win."

MORE: Steelers don't take Trump's bait

ESPN's Adam Schefter reported Sunday would be an "unprecedented" day of protests in the NFL. The public's collective eye was focused on how players would react to a series of tweets from Trump.

"If NFL fans refuse to go to games until players stop disrespecting our Flag & Country, you will see change take place fast," Trump tweeted at 6:44 a.m. ET on Sunday. "Fire or suspend!"

He followed that up 29 minutes later with another thought on the topic: "...NFL attendance and ratings are WAY DOWN. Boring games yes, but many stay away because they love our country. League should back U.S."

Those tweets were his fifth and sixth related to the NFL or NBA in less than 24 hours. Trump opened Saturday morning by saying the NBA champion Warriors would not be invited to the White House due to star Stephen Curry's "hesitating" about whether he wanted to go. Curry had reiterated the previous day he had no interest in visiting the president.

Trump then expanded on his comments at a Friday rally in Alabama, saying NFL players should stand for the anthem or "YOU'RE FIRED! Find something else to do!"

Several NFL team owners, and commissioner Roger Goodell himself, have responded to Trump's tweets with statements.

Contributing: Marc Lancaster