The Hoops boss is adamant that the Scottish Premier League remains his top priority and wants his players to share his view.
He told reporters: "There was just no excuse for the lack of quality in our overall performance.
"Up until that, our domestic form had been blistering. 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, andthey 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."
Celtic have a chance to improve their domestic form later today when they host St Johnstone in a Scottish League Cup quarter-final.