Trump criticized any of the league's players who might challenge the rule and continue to kneel in protest, suggesting "maybe you shouldn't be in the country."
"I don't think people should be staying in locker rooms," Trump said in an interview with "Fox and Friends" this morning. "You have to stand proudly for the national anthem or you shouldn't be playing. You shouldn't be there. Maybe you shouldn't be in the country. You have to stand proudly for the national anthem."
NFL Commissioner Roger Goodell announced Wednesday that all players and NFL team personnel "shall stand and show respect for the flag and the anthem" during the upcoming season.
Athletes who choose not to stand for the national anthem under the new policy will be allowed to stay in the locker room until the performance of the anthem is over, according to Goodell’s statement.
Personnel who’re not standing on the field will be fined.
After a season filled with controversy over players protesting peacefully by locking arms, kneeling or skipping the national anthem on the field, Trump lauded the NFL’s decision to fine teams for players who might choose to continue their dissent this season.
"The NFL owners did the right thing," he said.
San Francisco 49ers quarterback Colin Kaepernick sparked the protests in 2016 after he refused to stand during the national anthem and honor a song and a flag that he said "oppresses black people and people of color."
NFL stars joined Kaepernick later that season, seizing the opportunity during the "Star-Spangled Banner" to kneel and bring attention to social justice issues.
Trump fueled the controversy further during a rally in Alabama in September when he said, "Wouldn’t you love to see one of the NFL owners, when somebody disrespects our flag, to say 'Get that son of a b---- off the field right now'?"
His consistent disapproval of the league’s professional athletes, and even of the owners for not condemning their players, put him at the epicenter of the controversy.
"I have so many friends that are owners," Trump told Fox News in September. "I think they're afraid of their players, you want to know the truth. I think it's disgraceful. And they've got to be tough and they've got to be smart."
Responding to the decision Wednesday, the president of the NFL Players Union, which represents current and former players, said in a statement, "The balance between the rights of every citizen in our great country gets crossed when someone is told to just 'shut up and play.'"
After the NFL rule change, Trump took no credit for the league's rebuke of the player protests, saying, "this was not me."
"I think the people pushed it forward," he said. "This was not me. I brought it out. I think the people pushed it forward."
ABC News' Bill Hutchinson contributed to this report.