http://news.bbc.co.uk/sport1/hi/football/teams/c/celtic/7318430.stm
Uefa is examining videos appearing to show Celtic supporters involved in sectarian chanting in Barcelona.
A Uefa spokesman confirmed the footage included singing outside and inside the Nou Camp for the Champions League last-16 match on 4 March.
"We have received some footage showing Celtic supporters singing some alleged anti-Queen and pro-IRA songs - sectarian songs," he said.
"If the investigation is conclusive, a disciplinary case would be opened."
Several videos have been brought to Uefa's attention, including film of supporters at the 'fan-zone' designated for travelling supporters.
"We take care of all manifestations of sectarian singing," the Uefa spokesman added.
"The only condition is that it must be in the immediate surrounding area of the stadium. There was alleged sectarian singing inside the stadium.
"It will depend on the easiness of having these songs understood and the quest of finding other evidence."