Colin Kaepernick, the 49ers quarterback whose refusal to stand for the national anthem has rocked the NFL and ignited a fierce debate about patriotism, free speech and the American flag, says he has received death threats since he began his protest last month.

Kaepernick said on Tuesday that the threats have arrived “via a couple of different avenues”. He said he has not reported them to San Francisco 49ers security.

The 28-year-old acknowledged that the likelihood of such threats had increased since he began his protest at the end of last month. Kaepernick has been protesting against police brutality and racial oppression, and has not stood for the national anthem since the Packers-49ers pre-season game in late August.

“To me, if something like that were to happen, you’ve proved my point, and it will be loud and clear for everyone why it happened, and that would move this movement forward at greater speed than what it is even now,” Kaepernick said. “Granted, I don’t want that to happen, but that’s the realization of what could happen, and I knew there were other things that came along with this when I first stood up and spoke about it. That’s not something I haven’t thought about.”

Kaepernick sat for the Packers game on 27 August and spoke publicly about why he wished not to stand.

“I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color,” Kaepernick said at the time. “To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder.”

He has since kneeled for the Niners’ past three games.

Kaepernick’s stance has prompted many other athletes to show their support. Several other NFL players have sat, knelt, or raised fists during the Star-Spangled Banner, and World Cup winner Megan Rapinoe has chosen to kneel before US international soccer games. Scores of high school and college players have also picked up the cause.

But Kaepernick has not received universal support. Donald Trump said “maybe [Kaepernick] should find a country that works better for him”, while failed presidential nominee Ted Cruz said: “To all the athletes who have made millions in America’s freedom: stop insulting the flag, our nation, our heroes.”

Kaepernick said he was the target of racial slurs and other insults before last Sunday’s NFL game at Carolina.

“There’s a lot of racism in this country disguised as patriotism and people want to take everything back to the flag but that’s not what we’re talking about,” he said on Tuesday. “We’re talking about racial discrimination, inequalities and injustices that happen across the nation.”

Kaepernick also spoke about the shooting of Terence Crutcher, an unarmed black man, in Tulsa, Oklahoma, last week. Police video shows the 40-year-old Crutcher walking away from police officers and towards his SUV last Friday with his hands in the air. He then approaches the driver’s side of his vehicle, where an officer shocks him with a stun gun and another fatally shoots him.

Police had been called to the scene to respond to a report of a stalled vehicle. The officer who shot Crutcher, Betty Shelby, has been placed on paid leave.

“His car was broken down, he was looking for help and he got murdered,” Kaepernick said. “That’s a perfect example of what this is about. I think it will be very telling what happens with the officers that killed him because everybody’s eyes will be on this.”

He said that events like Crutcher’s death were precisely why he began his protest. “I find it very hard that people don’t understand what’s going on. I think the message has been out there loud and clear for quite some time now.”

On the Conan O’Brien show on Tuesday night, former Seahawks running back Marshawn Lynch said he supported Kaepernick’s stance.

“With what’s going on, I’d rather see him take a knee than stand up, put his hands up and get murdered,” Lynch said. “My take on it is … fuck, they got to start somewhere. I just hope people open up their eyes and see that there’s really a problem going on, and something needs to be done for it to stop.”