The NBA is investigating Hawks star Dejounte Murray for making contact with an official at the end of Game 4 against the Celtics Sunday in Atlanta ... and could be suspended as his team fights for their playoff lives.

As the game clock winded down in the fourth quarter at State Farm Arena, Murray and his teammates began leaving the court, but Dejounte made a detour, before heading for the locker room.

Check out the video ... Murray walks up to official Gediminas Petraitis, in his 8th season as an NBA ref, and appears to bump him with his chest. It's unclear if the contact was incidental.

Dejounte also appeared to say something to the ref, before starting to walk away. Seconds later, a visibly frustrated Murray turns around and starts pointing while yelling, ultimately having to be restrained by his teammates before leaving the court.

The Celtics took a commanding 3-1 series lead in the first round after defeating Atlanta 129-121 ... and will look to close out the series in Game 5 Tuesday in Boston.

And, they may have to do it without Murray. Per NBA rules, "intentional physical contact with an official" results in an automatic one-game suspension. Again, the question is, was it intentional?

Murray has been one of Atlanta's best players -- alongside superstar pg Trae Young -- averaging 25.3 points per game and 7.3 rebounds through four contests against the C's. Losing Dejounte, one of their most potent offensive threats, would be a considerable blow.