Some £10,000 worth of damage was caused to seating in the middle-lower south stand at Fir Park, just above where a Green Brigade banner was displayed. A flare was let off before the game, two smoke bombs thrown into the goalmouth, one landing yards from Celtic goalkeeper Fraser Forster, and a missile flew from the Celtic support not far over the head of the England goalkeeper after Kris Commons opened the scoring in Celtic's 5-0 SPFL Premiership win.
While they prepare to play Barcelona in their final Champions League game of the season on Wednesday, the Camp Nou fixture has, for now, been overshadowed by scenes Celtic described as "appalling".
Police Scotland are looking into the "significant damage" caused, and they said 18 smoke bombs, three fireworks and one flare were set off. No arrests were made inside Fir Park. Celtic have launched an investigation, while the Green Brigade fans group has condemned the vandalism and admitted it should have more effectively self-policed its section.
A Green Brigade statement read: "We do not condone the breaking of seats, nor do we welcome pyrotechnics being thrown on the park. We as a group are as disappointed as any about such indefensible behaviour and regret it happened on our watch.
"While it was not members of our group behaving in this manner, we accept that these actions took place behind our banner in what was an unofficial 'Green Brigade section' and furthermore that the fans within this area are associated to our group whether they are members or not. It is particularly disappointing given how hard we have worked as a member organisation of Fans Against Criminalisation and of our own accord to fight the criminalisation of football supporters as we realise the damage that the events of Friday could have on our efforts to challenge the continued harassment of Celtic fans by Police Scotland.
"Ultimately, we should have had greater control of the bodies present within our block and our failure to do so has resulted in events which are unacceptable. We will strive to ensure that such scenes are not repeated."
The main Celtic fans' group, the Affiliation of Registered Celtic Supporters Clubs, said in a statement: "We should be discussing another devastating performance by Celtic. Instead we are talking about disappointments off the field. Incidents like [Friday] night at Fir Park and the publicity this attracts makes any negotiations regarding ticket pricing, safe standing and policing at games more difficult.
"Any payment for damage and fines that are the responsibility of the club are ultimately paid by us. This is a measurable cost. The damage to our reputation as a support is unquantifiable. In a time when we are fighting to reduce ticket prices, fighting against the Offensive Behaviour Act and trying to make the game more attractive to the fans who have lost interest [Friday] night is nothing short of disheartening and does nothing to help."