Celtic could face UEFA sanctions after police raised concerns over chants sung by supporters during their recent Europa League game against Rennes at Parkhead.
It is understood that Strathclyde Police made the UEFA delegate aware of what they termed "offensive" singing during Celtic's 3-1 victory on November 3.
The news comes amid reports UEFA have opened a disciplinary case against Celtic over 'discriminatory chanting'.
A spokesman for Strathclyde Police said: "We can confirm there were a number of instances during the game of singing offensive songs and inquiries are ongoing to detect the offenders."
Neither UEFA nor Celtic's media departments were available for comment on Saturday but reports say the case will be heard on December 8.
Celtic last month urged fans to stop singing pro-IRA chants after being "inundated" with complaints from their own supporters following their 2-0 defeat by Hearts at Tynecastle.
Lothian and Borders Police announced they had launched an investigation into the "singing of sectarian songs" following the Clydesdale Bank Premier League game on October 2.
Celtic chief executive Peter Lawwell said: "Chants glorifying the Provisional IRA are totally unacceptable.
"One, it is wrong, and it is an embarrassment to the club and embarrassment to the majority of supporters.
"We have dealt with it at Celtic Park and we will do all we can to make sure it doesn't happen home or away. We don't want it, we don't need it. We have the best supporters in the world and hold that reputation dear."