The NFL’s brand has been “clearly damaged” over the controversy of players protesting during the national anthem, ad executive Harris Diamond said Wednesday.

Fans are annoyed by the political back-and-forth between President Donald Trump and the NFL players, and “that is a problem,” said Diamond, CEO of McCann Worldgroup, the world’s No. 2 ad agency.

“They obviously have to quiet it down,” Diamond told CNBC’s “Squawk Box.” “The NFL’s clearly been damaged. There’s no doubt about it.”

“At the end of the day, they need their players to believe that their teams believe in them. And this is obviously something that’s heartfelt, it’s emotional, it goes beyond business issues,” he added.

At an upcoming meeting, the league will discuss the nationwide dispute over whether players must stand during the national anthem, Commissioner Roger Goodell said in a copy of a memo obtained by CNBC.

Diamond didn’t say whether there was an “artful” way for the NFL to get past the controversy but said that at least “time heals all wounds.” “I do think that time will actually heal this,” Diamond said. “But the reality is we actually have to get beyond this.”

The firestorm started when then-San Francisco 49ers quarterback Colin Kaepernick kneeled during the national anthem last season to protest the treatment of African-Americans in the United States.

Trump later began tweeting about the issue and said players who don’t stand should be fired.

Earlier Tuesday, Trump tweeted that tax laws should be changed so that the NFL doesn’t get “massive tax breaks while at the same time disrespecting our Anthem, Flag and Country.”