New York (CNN) President Donald Trump drew the ire of professional athletes for comments he made at a rally in Alabama on Friday night and on Twitter on Saturday morning.

Trump first took aim at the NFL, saying team owners should fire players for taking a knee during the national anthem.

The President said owners should respond to players by saying, "Get that son of a bitch off the field right now, he's fired. He's fired!"

He doubled down on the comments on Saturday afternoon.

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.... — Donald J. Trump (@realDonaldTrump) September 23, 2017

...our Great American Flag (or Country) and should stand for the National Anthem. If not, YOU'RE FIRED. Find something else to do! — Donald J. Trump (@realDonaldTrump) September 23, 2017

Last year, Colin Kaepernick -- formerly with the San Francisco 49ers, but currently without a team -- drew national attention for refusing to stand during "The Star-Spangled Banner" prior to kickoff.