Players have been increasingly “taking a knee” in protest following remarks made by the president last week when he criticised the trend.
However, Mr Trump continued his onslaught against the NFL yesterday in a series of tweets, saying: “Ratings for NFL football are way down except before game starts when people tune in to see whether or not our country will be disrespected.”
He also said booing at the Dallas game on Monday night when the team dropped to its knees was the “loudest I have ever heard”.
Following a weekend of kneeling and protesting across the NFL, the Dallas Cowboys and their owner displayed their own version of unity on Monday by kneeling on the field before rising as a group ahead of the playing of the national anthem.
Mr Trump noted in his tweets that the team stood for the anthem. “Big progress being made – we all love our country,” he said.
Cowboys owner Jerry Jones has been a staunch supporter of Mr Trump, so the speculation was that he would not allow his players to kneel during the national anthem.
“I hope that I’m clear and I hope that our team is clear – we want to respect the flag. Make no mistake about that,” Mr Jones said.
“We also want to as a complete team, as players and an organisation, be able to, whenever we can, demonstrate that unity is important and equality is important.”
After warm-ups on Monday night, the Cowboys went into the dressing room and returned to the field for the anthem, lining up between the sideline and the yard markers on the field. They dropped to their knees as a giant flag was carried onto the field, with Mr Jones and his family in the middle. Boos rang out around the stadium.
The protests started more than a year ago when former San Francisco 49ers quarterback Colin Kaepernick refused to stand during the anthem in protest over police treatment of minorities.
They have since spread to other sports including the US women’s basketball league, and elsewhere, with musicians Stevie Wonder, Pharrell Williams and John Legend taking a knee last weekend.