Romanian and Bosnian fans clashed in the stands during their Nations League match at the Giulesti Stadium in Bucharest on Monday.
Flota Swinoujscie and Gwardia Koszalin fans clashed during their Polish fifth division match on Sunday.
Nice and Cologne fans clashed in the stands at the Allianz Riviera stadium before their Europa Conference League match on Thursday.
Borussia Dortmund and Copenhagen fans were seen throwing flares at each other before the start of their Champions League match at the Westfalen Stadium on Tuesday.
Ruch Chorzow fans clashed with stadium security during their Polish Cup tie against rivals Gornik Zabrze on Thursday.