Croatia's Euro 2016 match against the Czech Republic was held up for several minutes after their fans threw flares on to the pitch and began fighting among themselves on Friday.
Eight flares and other objects landed on the pitch near to riot police, who had been deployed in front of the section housing Croatia fans.
The trouble broke out in the dying minutes of a game that Croatia were leading 2-1.
UEFA said disciplinary proceedings would be opened on Saturday once they had received the official reports about the trouble from the match delegate and referee Mark Clattenburg
The English referee called the players to the centre of the pitch and consulted an official after the trouble broke out, while Croatia's players appealed for calm from the fans.
An announcement over the public address system at the Stade Geoffroy Guichard pleaded with the Croatia supporters to "leave the stadium and don't embarrass our country".
Play eventually resumed with the Czechs getting an equaliser with a penalty to salvage a 2-2 draw in the Group D match.
The drama left Croatia's frustrated players unhappy.
"We lost our pace when play was suspended because of our supporters," Ivan Rakitic, who made the score 2-0, said.
Ivan Perisic, who had put Croatia ahead, added: "I cannot understand why we have to waste out energy to calm our own supporters."
