The United star earned a second yellow card for a foul on the Saint-Etienne winger.
But the second-half dismissal in the Red Devils' Europa League round of 32 second leg in France seemed harsh.
Bailly saw red with United leading 4-0 on aggregate and 1-0 on the night, meaning he is now ruled out of the first leg in the next stage.
While Jose Mourinho was left angry over the incident, he did see a positive element.
Eric Bailly's red card against Saint-Etienne was his first ever dismissal for Manchester United
Hamouma has good qualities but he enjoyed too much the diving and the simulation
It means one of his back-up defenders who have impressed this term will get game time.
Either Marcos Rojo or Phil Jones – currently sidelined through injury – are expected to be drafted in as Bailly's replacement.
"Hamouma has good qualities but he enjoyed too much the diving and the simulation, so he gets in these situations," Mourinho said.
"Eric can't play the first match of the next round.
Manchester United boss Jose Mourinho accused Saint-Etienne's Romain Hamouma of diving last night
Man United fans react as Eric Bailly gets sent off against Saint-Etienne
Wed, February 22, 2017
Express Sport brings you all the best tweets as Manchester United fans react to Eric Bailly's red card against Saint-Etienne
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Eric Bailly is now suspended for Manchester United's round of 16 first leg in the Europa League
"Rojo came in and did well and hopefully Jones will be back soon.
"So one misses, it's an opportunity for another."
Mourinho's side will discover their last-16 opponents tomorrow in the Europa League draw at 12pm.
The first leg is scheduled for four days before Manchester United play rivals Chelsea in the FA Cup quarter-final at Stamford Bridge.