Neil Lennon has revealed that his "heart sank" when he saw the Green Brigade banner on Tuesday night prior to Celtic's Champions League encounter with AC Milan.

The Irishman believes that the sign had a negative impact on the atmosphere within the stadium since there were many other Hoops fans uneasy with the decision to make a political statement on the night of such a significant game.

Claiming that he felt "let down" by it, Lennon has urged the Green Brigade to put the club before anything else.

Celtic will be rapped by Uefa for the banner which will amount to a fine, but the sanction could be greater if the club are not seen to crack down on the issue.

"When I saw it, my heart sank," said the Celtic manager.

"I think it affected the atmosphere in the stadium. I think there was a lot of head-scratching from other quarters of the stadium. I understand that they have maybe legitimate reasons to complain about things or make statements about things but Tuesday night was not the time or the place.

"We don't know the next time we will be in the Champions League so those games should have been a celebration rather than a political protest by one section of the support. It was totally unnecessary.

"I think the club are quite sympathetic at times to their points of view but they assured us that there wouldn't be any political connotations on the banners and that proved not to be the case.

"Do I personally feel let down? Yes because I think it's tarnished the reputation of the club. "

Lennon also believes that it undermines the efforts of the club to go forward together.

"When I came in, I wanted to bring the club together again, and I think the players have done that," he said.

"We have had great success in the last three or four years. What is going to make people happy? I don't know.

"I don't think the club has been in a better position in a long, long time. Maybe not on the field, because that takes a lot of money, but we have good young players here. They're ambitious and want to do well for the club.

"In really difficult times financially, we're really robust. That's not easy in this day and age. We're solid for the future.

"We can't do any more and yet people still want to complain.

"It's not just costing us money in terms of fines, it's damaging the reputation of the club, and I don't like it."