United States President Barack Obama says San Francisco 49er quarterback Colin Kaepernick was exercising his constitutional right by not standing during the national anthem, although it might be a "tough thing" to stomach for people in the military or law enforcement.
Kaepernick sparked controversy last month when he remained seated through the traditional rendition of 'The Star-Spangled Banner' before a preseason game, and has continued with what he says is a protest against racial injustice and police brutality.
Many Americans have denounced the gesture as a sign of disrespect to the flag, although he has drawn support from some people, including some fellow players.
Speaking in China after a gathering of leaders of 20 leading economies, Obama said he did not doubt Kaepernick's sincerity in making the protest but acknowledged it was difficult for some to swallow.
"I think there are a lot of ways you can do it as a general matter when it comes to the flag and the national anthem and the meaning that that holds for our men and women in uniform and those who've fought for us. That is a tough thing for them to get past to then hear what his deeper concerns are," Obama said.
Kaepernick, who led San Francisco to the 2013 Super Bowl but has since been demoted to backup, is the latest professional athlete to use his celebrity to call attention to the issue of the mistreatment of minority groups by law enforcement.
Over the past two years, a series of police killings of African-Americans in cities across the country have triggered protests and given rise to the Black Lives Matter movement.
Despite the controversy, Obama said he would rather have engaged young people "trying to think through how they can be part of our democratic process than people who are just sitting on the sidelines and not paying attention at all".
Obama, speaking at a news conference, said he had not been following the controversy closely, but added, "If nothing else what he's done is he's generated more conversation around some topics that need to be talked about."
"Sometimes it's messy, but it's the way democracy works."
In a gesture of solidarity with Kaepernick, American women's soccer star Megan Rapinoe knelt during the national anthem at a Sunday match, calling it a deliberate move to support Kaepernick.
Some critics of the player say Kaepernick, 28, should be punished.
The National Football League has issued a statement saying it encourages players to stand during the anthem but does not require them to do so.
The 49ers have framed the issue in terms of the right of free expression enjoyed by all Americans.