'I just want the players to show a little more humility at times." This sentence was spoken so softly by Neil Lennon that it could have been construed as an appeal.

This would have been an erroneous impression. It was more of an order.

The defeat by Kilmarnock on Saturday precipitated a "frank discussion" with the Celtic squad on Sunday and precedes a meeting with St Johnstone tonight that bristles with danger.

Steve Lomas's side beat Celtic at McDiarmid Park last month in the Clydesdale Bank Premier League and a repeat in the quarter-final of the Scottish Communities League Cup would be devastating for a Celtic side that is routinely being linked with domestic trebles.

Lennon is far too cute to link himself with such ambitions publicly but his side's domestic lapses against St Johnstone and Kilmarnock have sparked much soul-searching and no little anger. The Celtic manager yesterday insisted the defeat on Saturday had made him the angriest he has been with his players and a meeting was convened on the training ground.

"We were always going to be in on Sunday, anyway, but we had a frank discussion. It was an unnecessary performance off the back of things going so well for us," said Lennon of the 2-0 defeat on Saturday. "It was a huge dose of reality. I just want the players to show a little more humility at times as well. But we have discussed it and it will not be mentioned again.

"I don't want to keep taking four steps forward and one back, or whatever it is. They have been playing some scintillating football and I just want them to get back to that.

"What surprised me was the drop in performance and tempo, compared to what it has been over the last three or four weeks. I didn't envisage us playing so poorly and so flatly, but that just shows you it can happen."

This inconsistency of performance is what irks Lennon most. Celtic were disciplined and defiant in the defeat by Barcelona, brilliant in defeating Spartak in Moscow and irresistible in Paisley in thrashing St Mirren.

Asked to expand on his call for humility, the Celtic manager said: "When things are going well I don't want them getting carried away. I'm not saying they are getting carried away but all the great teams have it [humility]."

Lennon cited Barcelona beating Rayo Vallecano 5-0 in the wake of a demanding Champions League tie. "The great teams just keep going, they don't rest on their laurels, sit back and say: 'I'm a good player, I have cracked it.' They just keep going the same way," he added. "They don't get too carried away with themselves, they have that even balance. That's what I want, they don't get too low when they get beaten and not too high when they win. I want a good response to Saturday."

The realisation of that order should be made easier by the inclusion of Scott Brown, the club captain, who has been training. "He was fit for the weekend but we decided after his exertions on Tuesday to give him a break," said Lennon.

"He wanted to play, we just weren't sure what reaction he would have got. With the amount of games we have coming up, it is a hectic schedule, we felt it might have been a good idea to give him a break at the weekend but obviously in hindsight it probably wasn't."

The manager repeated his post-match analysis that he was to blame for making too many changes but the depth of the Celtic squad has been taken as an accepted truth and it was alarming for supporters to watch a flat performance with Gary Hooper, Victor Wanyama and Brown rested.

However, Celtic brought in five internationalists – Adam Matthews, James Forrest, Biram Kayal, Kris Commons and Miku – and both fans and manager were entitled to be somewhat baffled by the level of performance.

However, Lennon had words of support for Miku, the 27-year-old Venezuelan striker who has failed to impress since signing on loan from Getafe. "He is taking his time to adapt to the rigours of the Scottish game but there was a lot of good stuff off the ball that he was doing," said the Celtic manager. "We didn't get the benefit of that because we were so pedestrian with the ball at times and lacklustre. So he can be excused, the rest can't."

However, the manager did point out: "He needs to adapt a bit more to the physical side of the game. He is not getting involved in the games enough for my liking, for a centre-forward."

Lennon will accept no excuses about the Champions League impacting negatively on domestic performances. "That's an easy way out. There was just no excuse for the lack of quality in our overall performance. Up until that, our domestic form has been blistering if you look at Motherwell, Hearts, St Mirren.

"It is a learning process for me because of the different demands and for the players, who are maybe playing Champions League for the first time. But we can't, and they can't, pin all their hopes on Champions League football and raise their game for these glamour games or whatever you want to call them. The SPL is the priority and if they are going to do that, then they won't play."

This is not so much a threat as a promise. Celtic players must find the way to humility tonight and a passage to the semi-finals.