The NBA has begun investigating whether James Harden’s absence from the Philadelphia 76ers’ season opener is a violation of the league’s new player participation policy.

The Sixers could be fined up to $100,000 if there is no approved reason for Harden to miss Thursday’s 118-117 loss to the Milwaukee Bucks – a nationally televised game.

Last offseason, the league issued a new participation policy to crack down on healthy players opting out of regular-season games, especially marquee matchups broadcast on ABC, ESPN or TNT.

“We're looking into the facts around James Harden's availability tonight to determine whether an approved reason exists for his lack of participation,” NBA spokesperson Mike Bass said in a statement.

Harden returned from a 10-day excused absence earlier this week and was told to report to the team’s practice facility to get into game shape while his teammates opened the season without him.

According to Bleacher Report’s Chris Haynes, Harden tried to board the team flight to Milwaukee but was stopped by a security official and left the airport.

An NBA probe is the latest development in a soured relationship between the 76ers and the 10-time All-Star.

In late June, Harden picked up his $35.6million player option for the 2023-24 season and then immediately requested a trade.

He could have declined the option and become a free agent but was hoping by exercising his option it would facilitate a trade.

He later blasted team president Daryl Morey in August while in China.

“Daryl Morey is a liar, and I will never be a part of an organisation that he’s a part of,” Harden said. “Let me say that again: Daryl Morey is a liar, and I will never be a part of an organisation that he’s a part of.”

Harden has since reiterated his unwillingness to play for Morey’s Sixers, but by reporting for practice this week, has shown some acknowledgement that his best chance at being traded would be to play well in Philadelphia until a partner is found.

The Los Angeles Clippers – widely considered Harden’s most likely destination – have suspended trade talks with Philadelphia, ESPN’s Adrian Wojnarowski reported Wednesday. Wojnarowski went on to report that the Clippers are the only team that has made a “serious offer” for Harden.