Uefa has opened disciplinary proceedings against four European football clubs Galatasaray, Basel, Arsenal and Borussia Dortmund.
While Galatasaray, Basel, and Borussia Dortmund are being probed for crowd disturbances in Champions League games, Arsenal is facing lesser charges of failing to stop flares entering their ground in Wednesday's 4-1 win over Galatasaray.
In Liverpool's tie in Basel, a battery appeared to be thrown towards the assistant referee, while flares were lit among Dortmund fans in Anderlecht.
The cases will be dealt with by Uefa's disciplinary body on 16 October.
Galatasaray, Basel and Dortmund could be fined or ordered to play behind closed doors if they are found guilty.
Arsenal face a possible charge of "insufficient organisation" as Uefa views the home side as responsible for searching supporters for any banned items, reports the BBC.
