US President Donald Trump has said basketball star LeBron James disrespected the US by not being still while the national anthem was sung.

James, who now plays for the Philadelphia 76ers, appeared to be practising a golf swing and basketball shots as the anthem was being performed ahead of the season opening match against the New York Knicks on Wednesday.

"While listening to our National Anthem, LeBron James disrespects our Country!," Trump posted on social media. "LeBron James should apologize to all of those Great American Warriors and Heroes who died for the American Flag."

James has not responded to the president's latest comments but the pair have criticised each other in the past.

James can be seen in a video making the motion of a golf swing as a performer sings the Star-Spangled Banner at New York's Madison Square Garden.

His teammates, who are lined up next to him on the court, mostly remain standing with minimal movement.

"I said right from the beginning that he's no good, a TOTAL DISGRACE," Trump added referring to James.

The US anthem is played on tape or performed at the start of most professional sports games. Players and spectators are expected to stand for it, if they can, and refrain from moving around. Some people sing along.

This tradition has become a political flash-point over the last 10 years. In 2016, former American football player Colin Kaepernick sat down and later knelt on one knee during the anthem, as a demonstration against police brutality and racism in the US.

Trump sharply criticised Kaepernick and later took credit when the athlete couldn't find a team to play for. Years later, he softened his stance saying Kaepernick should "get another shot" to play in the NFL.

The president's criticism also speaks to his longstanding feud with the popular player, who has publicly endorsed or campaigned for Trump's political opponents since the 2016 presidential election

In 2018, Trump suggested James wasn't an intelligent man after the athlete said he "would never sit across" from him.

That same year, James said Trump had given racists "an opportunity to be out and outspoken without fear."

He has also suggested that Trump's rhetoric led to a mob storming the US Capitol in 2021 to stop the certification of the result of the 2020 election, which former President Joe Biden won. James had endorsed Biden.

In July, when asked to choose between James and Michael Jordan as the all-time greatest basketball player in history, Trump said he preferred Jordan and suggested James, who is black, might be "a racist".

"I only like people that like me," Trump said.