City lead the round 16 tie 3-1 from the first-leg.
Guardiola said: "I know that the 1-3 against Copenhagen is a good result, but in the group stage we did the same thing with Leipzig, then in the second leg we were 2-0 down. A red card or anything else could complicate things, so we have to be careful even if we start from a favorable result."
Advertisement
Advertisement
Guardiola also praised Phil Foden, one of City's best in recent weeks: "He will be a legendary player because in a short time he has played many matches, scored many goals and won many titles.
"He is a player from our youth sector and that's why he has an incredible bond with the fans."