The incident occurred during Celtic's 4-3 defeat in Croatia, in the final Group D encounter.
UEFA released a statement on Tuesday declaring that the Scottish Premier League leaders are being investigated, although a final decision will not be reached until the week of Celtic's last-32 meeting with Inter in February.
A UEFA release read: "Disciplinary proceedings have been opened following the UEFA Europa League group D match between GNK Dinamo Zagreb and Celtic FC (4-3), played on 11 December in Croatia.
"Celtic FC: Charges: Crowd disturbances - Article 16 (2) (h) of the UEFA Disciplinary Regulations.
"The case will be dealt with by the UEFA Control, Ethics and Disciplinary Body on 19 February 2015."
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
