- American president's swipes at NFL star Kaepernick, NBA superstar Curry stokes fierce response on social media.

U.S. President Donald Trump faced biting criticism Saturday, even from NBA superstar LeBron James, after he targeted prominent athletes in two of the world's best-known sports leagues for expressing their political views.

Trump used a campaign podium in Alabama on Friday to attack NFL star Colin Kaepernick, whose silent protest -- where he takes a knee during the national anthem before games -- has become a national phenomenon that has inspired many other athletes to follow suit, while sharply dividing public opinion.

“Wouldn’t you love to see one of these NFL owners when someone disrespects our flag, to say, 'Get that son of a bitch off the field right now. He’s fired. He's fired!'" the president yelled in the microphone to roaring applause from his supporters.

Trump went on to say he believes that one of the owners -- who are "friends of mine, many of them" -- would eventually do it.

"They don’t know it. They’ll be the most popular person in the country for a week. They’ll be the most popular person in the country," he said.

DeMaurice Smith, the executive director of the NFL Players Association, issued a statement on Twitter saying that the union "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".

Current and former players weighed in on Trump's attack as well. Cincinnati Bengals safety George Iloka tweeted: "I can’t take anything our Celebrity in Chief says seriously. He’s a real life clown/troll."

Minnesota Vikings running back Bishop Sankey said, "It's a shame and disgrace when you have the President of the US calling citizens of the country sons of a bitches," in a tweet liked nearly 25,000 times.

On Saturday, Trump found himself in hot water again after he attacked 2017 NBA champion and Golden State Warriors superstar Stephen Curry for saying he did not want to participate in the traditional White House championship visit.

Trump tweeted in response: "Going to the White House is considered a great honor for a championship team. Stephen Curry is hesitating, therefore invitation is withdrawn! "

Cleveland Cavaliers All Star shooting guard LeBron James -- considered among the greatest players in NBA history -- defended Curry, whose Warriors defeated LeBron's Cavaliers in the 2015 and 2017 Finals, with a harsh tweet that was liked over a million times.

"U bum," James wrote. "@StephenCurry30 already said he ain't going! So therefore ain't no invite. Going to White House was a great honor until you showed up!"

He later explained in a video why he felt the need to respond to President Trump. "I think this is basically at a point where I am just a little frustrated, man," he told Uninterrupted. "This guy that we have put in charge has tried to divide us once again."

James referenced the white supremacist, neo-Nazi protest in Charlottesville, Virginia that claimed the life of a young woman, injured others and gave the American society pause about the state of race relations under the Trump administration.

"It is now hitting home even more for me because he is now using sports as the platform to try to divide us," James said.