Wolverhampton Wanderers fans were attacked by a group of Standard Liege hooligans in the Portuguese city of Porto on Tuesday night.
Celtic fans were attacked outside a pub in Rome ahead of their side's Europa League meeting against Lazio on Thursday night.
Karpaty Lviv and St. Etienne hools clashed in a mass fight in the western Ukrainian city of Lviv on Wednesday night ahead of the French side's match against Oleksandriya in the Europa League.
Young Boys and Feyenoord fans clashed briefly in the Swiss capital on Thursday ahead of their Europa League fixture.
Strasbourg and Eintracht Frankfurt fans clashed at a tram stop after Thursday night's Europa League match.
Hajduk Split fans invaded the pitch to vent their displeasure following the side's 3-1 home defeat to Maltese club Gzira United on Thursday.
Levski Sofia and Cracovia hooligans clashed in a mass fight in Bratislava on Wednesday.
Football hooliganism has returned to the Europa League with a bang after a two-month break.
Slavia Prague fans clashed with stewards inside the Parken Stadium after the side's Europa League match against FC Copenhagen on Thursday night.
Sparta Prague's Europa League second qualifying round tie against Spartak Subotica was briefly halted on Thursday after a group of Sparta hooligans broke onto the pitch.
Marseille fans clashed with riot cops in the Old Port area of the southern French city after their team's defeat to Atletico Madrid in the Europa League final on Wednesday night.
Athletic Bilbao and Spartak Moscow fans clashed on the streets of the Basque city ahead of their Europa League match on Thursday night.