They did well in the qualifiers against Helsinki and Helsingborg. But the standard they will face against Spartak Moscow will be far higher.
There will be the familiar face in Aiden McGeady and Lennon knows his capabilities.
Spartak are a quality side and, given the way they played against Barcelona in the opening game, Celtic can expect to get it tough on Tuesday night.
The biggest thing is getting off to a good start. It is vital you keep it tight for the first 20 minutes.
Against Benfica, concentration levels were high and discipline and application was good. Those qualities will need to be in evidence again on Tuesday evening.
Neil's side have been progressing well but it will take an excellent performance if they are to come away from Russia with a positive result.
One of the main plusses for me this season so far has been Kelvin Wilson. He has looked very steady since that game at home to Helsingborg and looks far more convincing playing at this level.