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.
Aberdeen fans clashed with stewards and riot cops after the Scottish club's 2-0 defeat at Apollon Limassol in Larnaca last night.
The start of Thursday's Europa League match between Lyon and Beşiktaş was delayed by fighting, pyrotechnics, and chaos caused by fans at the Parc OL.
Austria Vienna and Spartak Trnava fans briefly clashed near the Ernst Happel Stadium ahead of their Europa League match on Thursday.
Fans of both teams clashed inside the St Jakob-Park stadium prior to kick-off.
Manchester United and Liverpool fans clashed in the stands at Old Trafford.