The Fox television network's broadcast of the day's first game, at Wembley Stadium, showed three members of the Miami Dolphins kneeling as US music star Darius Rucker performed "The Star Spangled Banner".
More than 200 players either knelt or used other means as expressions of unity last weekend.
Other teams, such as the Lions and Jets, opted to lock arms during the national anthem.
The controversy over NFL players taking a knee during the national anthem is showing no sign of letting up.
The entire Dallas Cowboys roster and coaching team, including owner Jerry Jones, knelt down in Arizona - which drew a hostile reception from the home fans - while the Pittsburgh Steelers, Tennessee Titans and Seattle Seahawks all chose to remain in the tunnel until the anthem had finished. "Respect our Flag and our Country!"More news: Five injured in suspected terrorism in Edmonton
"Very important that NFL players STAND tomorrow, and always, for the playing of our National Anthem", he wrote.
Ryan also acknowledged that the original point of the player demonstration - racial injustice and police mistreatment of African-Americans - has become obscured by the narrower issue of how to act during the anthem. [NL2N1M40CQ] Some African-American players adopted the symbolic gesture of kneeling during the anthem over the previous year to protest against racial disparities in the US criminal justice system. He says "most people agree" with him. I wonder how many of them know what the issue is. "I think they made it clear they support our players, but also support our country, the national anthem, the flag-all of the things some have suggested we don't".
National Football League spokesman Joe Lockhart called the president's statements "inaccurate". No Falcons players were kneeling during the national anthem. The protests culminated a week ago when scores of players, following calls by the president to fire protesting athletes, sat or knelt as the anthem was played.
"The owners are clearly united in a sense that the attacks on the game, on the NFL, on the players were unfair and unfounded, and that there was unity among the group", Lockhart said, noting that about two-thirds of the 32 team owners were at league headquarters this week for committee meetings.
"But as I said in my Twitter post, it's bigger than me".