Celtic play their second game in Champions League Group C when they face Manchester City at Parkhead this evening, kick-off 7.45pm.
Brendan Rodgers' side began with a heavy defeat in Barcelona while the English Premier League leaders beat Borussia Monchengladbach 4-0 on matchday one.
The Celtic boss, whose side thrashed Kilmarnock 6-1 on Saturday, said: "I have watched Man City and worked against them and they have always had an outstanding group of players but the level of their play has gone up since Pep (Guardiola) has come in.
“We know it’s going to be a difficult night but we hope it’s going to be a difficult night for them. Celtic Park, traditionally, is a very difficult place to come and play. One thing’s for sure - we won’t be as passive as we were in the last game.”