Celtic have been charged by UEFA over crowd trouble during their Europa League win over AIK in Stockholm.
The club are being investigated after fans let off flares in the away end and missiles were allegedly thrown as the Hoops triumphed 4-1.
The Swedes also face punishment concerning blocked stairways following last Thursday's playoff tie at the Friends Arena.
There were clashes between fans and stadium security and that prompted Parkhead chiefs to lay the blame on supporters of AIK's rivals Hammarby.
It was claimed the Swedes had infiltrated the away end and sparked trouble. Video later emerged of fans fighting with police, with batons used on supporters.
The incident was included in the match delegate's report and Celtic could now be punished.
A statement on UEFA 's website said: "Disciplinary proceedings have been opened following the UEFA Europa League play-off second-leg match between AIK and Celtic FC (1-4), played on 29 August in Sweden."
UEFA will deliver their verdict after a hearing on September 19.
The Parkhead club vowed to fight their case and last week promised their own investigation into events.
A Celtic spokesman said: “The club intends to launch a full investigation into the events in Stockholm.
“But the initial reports and intelligence we have gathered suggests that local supporters from a rival club may have been responsible for the unfortunate disturbances we witnessed.
"If that is indeed the case then obviously Celtic will strongly defend the reputation of our own supporters.
“We are concerned that AIK sold tickets to locals in that section. It was clear many Hammarby fans were in the Celtic sections and this was raised by Celtic officials before the match.
“A lot of Swedish fans managed to infiltrate the away section which we believe was a major factor in the issues which arose. There was a lack of control at the access points to the Celtic section.
“We are aware that a number of Swedish supporters entered the area for visiting fans and we are currently investigating events.”
