NBA executive vice president Stu Jackson said the foul, initially ruled a flagrant foul, penalty one, has been reviewed by the league and changed to a more serious penalty two.
The foul caused Marion to lose his balance while attempting a fast-break layup. He crashed into photographers on the baseline, hurting his right ribs.
At practice in suburban New Orleans on Thursday, before Belinelli was fined, Hornets coach Monty Williams said he thought officials got the initial call right.
"Marco's foul on Marion -- he has the same play against [Mike] Conley in Memphis and he allows Conley to get a layup -- I talked to him about we're not trying to hurt anybody, but you don't give up layups," Williams said. "I thought it was a good foul. He didn't try to hurt him."
Marion stayed on the court for a few possessions after the play, which occurred in the third quarter, then left the game for good.
Marion said afterward that X-rays were negative and that he'll be fine.
Belinelli wound up scoring 21 points, including his fourth 3-pointer of the game with 50 seconds left, igniting an improbable 8-0 run during the final minute.
Had officials initially ruled a flagrant foul, penalty two, Belinelli would have been ejected with more than 5 minutes remaining in the third quarter.