Donald Trump predicted on Wednesday that the National Football League will 'go to hell' if they don't listen to his demand for a ban on protests during pre-game playing of the National Anthem.

That pronouncement followed a stinging rebuke of the league Tuesday night during a Republican Party fundraising dinner in New York, where he blasted NFL executives for picking and choosing what kind of social-awareness campaigns are allowed on the field.

'They have a rule, you can't dance in the end zone, you can't wear pink socks – one guy's mother had breast cancer and they wouldn’t let him – you can’t do anything,' he carped, according to a report in Politico.

'But you're allowed to sit down for the National Anthem!'

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President Donald Trump warned National Football League owners that their business will 'go to hell' if they don't listen to his demand for a ban on protests during pre-game playing of the National Anthem.

Many Buffalo Bills players took a knee during the playing of the National Anthem prior to their game Sunday against the Denver Broncos

Trump told reporters before leaving the White Houe Wednesday for Indiana that what began more than a year ago with a lone NFL quarterback protesting police brutality has gotten out of control

Trump addressed the case of former San Francisco 49ers quarterback Colin Kaepernick, who started the trend of taking a knee instead of standing for the anthem, as a protest of police officers' treatment of black suspects.

'All [NFL Commissioner Roger] Goodell had to do was say, "There's rules and you can't do it," suspend him for a couple games. You would never have had this,' he said.

On Wednesday as he left the White House for a tax reform speech in Indiana, Trump doubled and tripled down on the firestorm he created last Friday during a speech in Alabama.

'I think the NFL is in a box,' he told reporters on the South Lawn of the White House as Marin One's rotors whirred. 'I think they're in a really bad box.'

Trump said Tuesday night at a Republican fundraising dinner that NFL Commissioner Roger Goodell (pictured) should have issued a rule against National Anthem protests

'You look at what's happening with their ratings. You look at what's going on. I mean, frankly, the only thing doing well in the NFL is the pregame because everybody wants to see what's going on.'

'You cannot have people disrespecting our National Anthem, our flag, or our country, and that's what they're doing' the president added.

'And in my opinion, the NFL has to change. Or you know what's going to happen? their business is going to go to hell.'

The Nielsen company, a firm that tracks television ratings, said Tuesday that NFL viewership has dipped 11 per cent this year, compared with the 2016 season.

'Most importantly, the fans agree with me,' Trump said, before catching himself and saying: 'I mean, largely the fans agree.'

Colin Kaepernick (right), a former San Francisco 49ers quarterback, started the kneeling trend last year and it quickly grew after Trump condemnation of it last week

The president, shown deplaning in New York prior to Tuesday night's fundraiser, said there are better places and times for NFL players to protest

'When they're protesting during a football game, I think they can find better places. But they cannot do it during the National Anthem.'

The majority of Americans do agree that professional athletes 'should be required to stand during the anthem at sporting events', according to a new Reuters/Ipsos poll.

The September 25-26 survey found that 58 per cent of those quizzed think athletes should stand while The Star-Spangled Banner is played or sung.

But 57 per cent of adults also said that they do not think the NFL should fire players who kneel instead.

On Tuesday during a joint press conference with Spanish Prime Minister Mariano Rajoy, Trump called the kneeling trend 'disgraceful.'