NFL commissioner Roger Goodell has described comments made by United States president Donald Trump regarding national anthem protests as "divisive".
On Friday Trump told a crowd at a rally that NFL owners should fire players if they refuse to stand during the national anthem.
"Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say, 'Get that son of a b**** off the field right now. He is fired'," Trump said.
Trump also lamented efforts by the NFL to make the game safer, adding: "Today, if you hit too hard... 15 yards, throw him out of the game. They are ruining the game, right?"
Responding in a statement, Goodell said: "The NFL and our players are at our best when we help create a sense of unity in our country and our culture.
"Divisive comments like these demonstrate an unfortunate lack of respect for the NFL, our great game and all of our players, and a failure to understand the overwhelming force for good our clubs and players represent in our communities."
Earlier the head of the NFL Players Association DeMaurice Smith posted on Twitter: "We will never back down. We no longer can afford to stick to sports."
We will never back down. We no longer can afford to stick to sports. pic.twitter.com/Ec3Bc4qt9h-- DeMaurice Smith (@DeSmithNFLPA) September 23, 2017
Attached to the tweet was a statement that read: "Whether or not Roger and the owners will speak for themselves about their views on player rights and their commitment to player safety remains to be seen.
"This union, however, will never back down when it comes to protecting the constitutional rights of our players as citizens as well as their safety as men who compete in a game that exposes them to great risks."
Trump has since reiterated his stance on Twitter, posting: "If a player wants the privilege of making millions of dollars in the NFL,or other leagues, he or she should not be allowed to disrespect our Great American Flag (or Country) and should stand for the National Anthem. If not, YOU'RE FIRED. Find something else to do!"
On Saturday Trump rescinded the Golden State Warriors' invitation to visit the White House after Stephen Curry stated that he did not want to go.
It was reported in June that Warriors players had unanimously voted against accepting a White House invite after their NBA Finals win over the Cleveland Cavaliers.