President Donald Trump says protests during the national anthem at NFL games leave the league in "a very bad box." (1:02)

President Donald Trump said Wednesday that the NFL is in a "very bad box" over the issue of players protesting during the national anthem and suggested it will harm the league's business.

"I think the NFL is in a box; I think they're in a really bad box," he said to reporters while leaving the White House for a trip to Indiana. "You look what's happening with their ratings, 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, our country, and that's what they're doing," Trump said. "And in my opinion, the NFL has to change. Or you know what's going to happen? Their business is going to hell." President Donald Trump said Wednesday that players protesting during the national anthem has left the NFL "in a really bad box." Rey Del Rio/Getty Images

The Nielsen company said Tuesday that through three weeks, viewership for national telecasts of NFL games was down 11 percent this season compared to 2016.

Nielsen said the games averaged 17.63 million viewers for the first three weeks of last season and have dipped to 15.65 million this year. The Nielsen figures don't include many of the Sunday afternoon games that are shown to a regional audience but not a national one.

Trump has, since late last week, been lashing out at NFL players who kneel during the anthem. The president first said the NFL should fire players who kneel, then tweeted that the players were being disrespectful of the American flag, the anthem, military personnel and the country.

He has also suggested that viewers are turned off by the protests and has suggested fans boycott the NFL.

Players have said the protest, which began with then-49ers quarterback Colin Kaepernick refusing to stand for the anthem, is their way of protesting racial inequality and police brutality. While the protests were scattered before Trump's comments, they spread to nearly every team in the NFL this past weekend. Players across the country linked arms or knelt during the anthem, and some were joined by their owners on the sidelines.

Three teams -- the Seahawks, Titans and Steelers -- opted to remain off the field during the anthem, though the Steelers said Monday they remained in their locker room to avoid a political statement, not as a protest.

Information from The Associated Press was used in this report.