Neil Lennon has hit out at the Celtic fans who sullied the club during the Europa League clash with Udinese.
Uefa may punish Celtic after flares were released by travelling supporters in Italy and a banner was unfurled criticising the governing body.
"I'm very disappointed; they have let me down, they have let the board, players and staff down and 99.9% of the support down," said the manager.
"My only surprise is that they got the spelling [on the banner] right."
Having questioned the intelligence of those who produced the banner, Lennon added: "The team covered themselves in glory last night and yet there is a rogue element who keep tarnishing the name of the club.
"The ironic thing is normally in the past when we come away from European games away from home we talk about how the team haven't done themselves justice and the fans always do.
"Now we are talking about the opposite."
Earlier, chief executive Peter Lawwell vowed to "weed out" supporters who continue to hurt Celtic.
And the club have imposed a lifetime ban on one supporter who was at the Stadio Friuli.
Lawwell told BBC Scotland that Celtic will face the consequences next week.
"These people are not Celtic supporters and we will weed them out. We are embarrassed," he said.
Uefa fined Celtic £12,700 earlier this week for "illicit chanting" by some of their fans in the home Europa League game against Rennes.
The Scottish club decided not to appeal against the fine.
Lawwell said the actions of some supporters "overshadowed a fantastic performance" in Italy, adding that "we have to get these people out of Celtic Park".
"These guys who had the banner: we will root them out, weed them out and they're not Celtic supporters," he went on.
"We will do all we can to identify them and take appropriate action. It's a very small minority; a rogue element have clearly infiltrated the support over the past six months to a year.
"The vast majority of Celtic supporters are positively supporting Celtic. We've gained a magnificent reputation around Europe and this, unfortunately, is an embarrassment that we can't tolerate and will eliminate."
Chairman Iain Bankier echoed Lawwell's views, saying: "We have to drive this out of the club.
"It's not only doing us harm, it's doing the whole of Scottish football immense harm.
"It's one or two, silly juvenile boys doing childish prank stuff and it's overtaking what was a fantastic performance."
Bankier then appeared to play down the previous Uefa fine, which was for pro-IRA singing at Celtic Park.
"It's doubly disappointing, coming right on the heels of a fine over something which was, in the whole scheme of things, not a major fault. Nevertheless, it was a technical offence and we took the fine."
Celtic exited the Europa League on Thursday after a 1-1 draw with Udinese.
Lennon's side surrendered a lead before half-time and failed to find a winner to reach the last 32.
Gary Hooper put Celtic into the lead inside 30 minutes with a close-range tap-in that was cancelled out on the stroke of half-time by Antonio Di Natale's clinical finish.