Manchester United could face UEFA sanctions after tens of flares were lit in the away end at Old Trafford during their Europa League clash with Saint-Etienne on Thursday night.
Supporters of the French club managed to smuggle pyrotechnics into the ground for their 3-0 Europa League defeat.
Smoke billowed from their section immediately before kick-off, with two flares thrown towards the playing surface.
UEFA take such incidents seriously and usually issue charges. Ultimately, it is United's responsibility to make sure no flares enter the stadium.