The Celtics will be without Grant Williams for one game -- the NBA just suspended the forward after making contact with a referee during Boston's matchup against the Bulls this week.
The call was made during the 4th quarter of the Celtics game on Oct. 24 ... after Williams was charged with a blocking foul against Zach LaVine.
The 6'6" baller disagreed with the call and unintentionally bumped into referee Cheryl Flores as he got up with frustration.
Williams was immediately ejected for making contact ... and he was so pissed, he had to be forced into the United Center tunnel by Celtics coaching staffers.
The NBA's Executive VP Joe Dumars announced Williams was suspended for one game without pay "for recklessly making contact with and directing inappropriate language toward a game official."
This means Williams -- who's averaging 9.5 points and 4.3 rebounds per game so far this season -- will be out for Friday's game against the Cleveland Cavaliers ... leaving the Celtics without one of their key role players in a tough matchup with an Eastern Conference opponent.