United States president Donald Trump has once again chimed in on the debate of protesting during the national anthem as he queried NFL commissioner Roger Goodell's recent statement.

Four years ago Trump was critical of former San Francisco 49ers quarterback Colin Kaepernick when he took a knee as The Star-Spangled Banner played to protest police brutality and racial injustice.

Those issues have again been brought to the fore recently following the death of George Floyd, with several high-profile NFL players including Patrick Mahomes and Michael Thomas creating a powerful video that asked the league to condemn racism and admit it was wrong for "silencing our players from peacefully protesting".

A video from Goodell in response conceded the NFL was "wrong for not listening to NFL players earlier" as he said they were encouraged to peacefully protest.

Though there was no direct reference to taking a knee for the anthem or refusing to stand, Trump reiterated his stance on the topic in a Twitter post.

He wrote: "Could it be even remotely possible that in Roger Goodell's rather interesting statement of peace and reconciliation, he was intimating that it would now be O.K. for the players to KNEEL, or not to stand, for the National Anthem, thereby disrespecting our Country & our Flag?"

Trump has previously suggested NFL owners should fire any players who kneel for the anthem.

Kaepernick has been out of the league since the end of the 2016 season but veteran running back Adrian Peterson said he was "without a doubt" planning to take a knee when the next campaign commences in September.