US President Donald Trump has accused basketball star LeBron James of disrespecting 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.

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

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.