Arsenal, Galatasaray, Basel and Borussia Dortmund face action
Uefa has opened disciplinary proceedings against Galatasaray, Basel and Borussia Dortmund after crowd disturbances in Champions League games.
Arsenal face lesser charges for failing to stop flares entering their ground in Wednesday's 4-1 win over Galatasaray.
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.
The Metropolitan Police has confirmed there were six arrests at the Emirates, two of which were for entering the ground with flares.