UEFA have confirmed they will investigate the incidents which marred Manchester United's Champions League win against Lille.
French police were criticised by fans for being heavy-handed at the Stade Felix-Bollaert, and tear gas was used during the match.
The investigation will also look at possible ticketing problems which led to supporters appearing to be in danger of being crushed against a 10-foot high safety barrier.
A statement from Europe's governing body read: 'UEFA has officially opened an investigation into events at the UEFA Champions League first knockout round first-leg match between Lille and Manchester United in Lens on Tuesday night.'
UEFA's control and disciplinary body will discuss the safety and security issues on March 22, more than two weeks after the second leg of the last 16 tie.
The date effectively rules out the expulsion of the French side from the tournament in the way Feyenoord were kicked out of the UEFA Cup this season for crowd disturbances.
United lead the tie 1-0 following Ryan Giggs' quickly-taken free-kick which almost led to Lille players walking off the pitch in protest.
Lille president Michel Seydoux vowed after the game to contact UEFA president Michel Platini and is expected to lodge an official protest.
UEFA officials are set to discuss the behaviour of the French side on Friday.