Neil Lennon has told Celtic fans that political statements have no place inside the club's Parkhead stadium.
The Hoops boss hit out after a group of supporters – known as the Green Brigade – displayed banners featuring Scottish historical figure William Wallace and IRA hunger striker Bobby Sands, who died in the Maze prison in 1981, during Tuesday night's Champions League fixture with AC Milan.
Those, along with other banners which had the words: 'The terrorist or the dreamer, the savage or the brave, depends whose vote you're trying to catch or whose face you're trying to save' were a protest against Scottish Parliament's attempts to rid the game of sectarianism by making "expressions of Irish identity, culture and politics" illegal.
Lennon, who was himself the victim of sectarian abuse from a section of Northern Ireland fans – and who received a loyalist death threat after he joined Celtic as a player – said: "It is not guaranteed you will play in the Champions League every year and my heart sank a little bit I have to say.
"I think there were a lot of other areas of the stadium where the supporters were scratching their heads and trying to understand the reasoning behind it.
"Since then we know the reasons behind it, but it certainly wasn't the time or place for a display like that.
"I don't know what you can do about it. It is certainly not welcome within the stadium. We understand that they maybe have legitimate complaints over some of the laws being brought in but Celtic Park is not the place to bring banners in like that."
Lennon continued: “It should have been a celebration rather than people having a grumble about something.
“When I came in here I tried to bring the club together again and I think we have done that, certainly with the performances over the last three or four years, so it is disappointing that some people want to bring cracks to the club.
“We are a football club at the end of the day, multi-cultural as well, so I think we need to put a stop to it.”
Uefa’s control and disciplinary body will look into the case on December 11 after confirming proceedings had been opened for “an incident of a non-sporting nature (illicit banner)”.
It is the fourth time in two years that the club has been the subject of investigation in relation to the behaviour of fans.
Celtic chief executive Peter Lawwell accused the Green Brigade of showing ‘clear disrespect’ to the club.
The defeat to Milan means Celtic can no longer qualify for the knockout stages of either the Champions League or Europa League, leaving Lennon to concentrate on domestic matters, starting away to Hearts in the fourth round of the Scottish Cup tomorrow.
“We want to win it,” he said. “The best thing the players can do is get back on to the pitch.
“There is a good atmosphere there and anything can happen on the day but I am expecting us to play very strongly and try to prevail.”
Midfielder Beram Kayal will miss the game after he was ruled out for six weeks with a broken bone in his foot.
On the Champions League exit, Lennon said: “What is success for us in the Champions League? It is only three times in 14 years (qualified for the last 16) and a lot of managers had a lot more money than me and didn't do it.
“We have to be careful about throwing money at things.
“We have to make sure we have a club that can compete every year in the Champions League.
“If we can make the last 16, fantastic, but it takes a lot of money to do that.”