Trump posted a video of the basketball legend doing apparent warm-up movements while lined up with his Philadelphia 76ers teammates.
"While listening to our National Anthem, LeBron James disrespects our Country! I said right from the beginning that he’s no good, a TOTAL DISGRACE," Trump wrote on his Truth Social network.
"LeBron James should apologise to all of those Great American Warriors and Heroes who died for the American Flag, and all that our Country stands for!" he wrote.
The video used by Trump had an internal caption that read: "LeBron working on his golf swing pregame." It showed him doing lateral swing motions and basketball shooting movements.
It was not immediately clear when the video was filmed.
There was no immediate reaction from James, 41, who is entering a record-extending 24th NBA season with his fourth team, or the 76ers.
Trump has been critical of athletes before for their behaviour during the playing of the US national anthem before games.
During his first term, Trump singled out NFL star Colin Kaepernick for his decision to kneel during the "Star-Spangled Banner" to protest racial injustice and police brutality.