J.J. Watt said kneeling for the United States national anthem "isn't disrespecting the flag or our military" as he fired back at a Twitter user who suggested he would not be among the Houston Texans players protesting.
The idea of taking a knee for The Star-Spangled Banner before NFL games to protest police brutality and racial injustice has been raised again following the death of George Floyd in police custody on March 25.
When former San Francisco 49ers quarterback Colin Kaepernick knelt four years ago he was heavily criticised by United States president Donald Trump, but the NFL recently apologised for not listening to its players and encouraged them to "speak out and peacefully protest".
New Orleans Saints quarterback Drew Brees was criticised for suggesting those who took a knee were "disrespecting the flag", though he later apologised for those comments, a U-turn that Trump insisted he was wrong to make.
The 2020 NFL regular season is not due to begin until September, but Texans head coach Bill O'Brien has said he would join his players in kneeling.
"Yeah, I'll take a knee," he told the Houston Chronicle.
"I'm all for it. The players have a right to protest, a right to be heard and a right to be who they are.
"They're not taking a knee because they're against the flag. They're taking a knee because they haven't been treated equally in this country for over 400 years."
A Twitter user responded to that story on the social media channel by writing: "Pretty sure you won't see @JJWatt taking a knee...." along with three emojis of the American flag.
However, Watt hit back from his own account, saying kneeling for the anthem had nothing to do with either the USA flag or the country's military.
He quote-retweeted his mention, saying: "A) don't speak for me B) if you still think it's about disrespecting the flag or our military, you clearly haven't been listening."
The new NFL regular season will kick off with the Texans facing the Kansas City Chiefs, who are the reigning Super Bowl champions, on September 10.
Houston have won the AFC South in each of the previous two campaigns but were beaten by the Chiefs in the playoffs last year.