Maresca won his first seven Premier League games as Manchester City manager but has now lost the last three.
Defeat to Nottingham Forest marked just the second time City have lost three back-to-back-to-back Premier League games in the past ten years.
Forest defender Jair Cunha opened the scoring with a brilliant solo effort with a Liam Delap brace rounding off the scoring for the home side.
Rayan Cherki scored City’s only goal of the game with a thunderous strike from just inside the Forest box.
Despite the defeat, City remain second in the Premier League but are now six points off table toppers Arsenal.
Speaking to BBC Sport after the game, Maresca said: "It's quite clear - first half we didn't match intensity or win duels or second balls.
“First thing required in these games is intensity. We tried to react at 2-0 but it's too late. We scored one, probably could have scored more but in transition we concede one more."
Why was intensity low? "I need to analyse that. Today's game is probably the first that we lack intensity in the first 45 minutes. Second half better. Never happened before - we need to understand the reason why and try not to let them happen again.
"First one is a consequence of the way we want to play. We want to play from the back so this can happen. Second and third goals quite similar - we lost the duel then concede on transition.
"We are conceding too many goals unfortunately and we need to improve that."
How to change that: "(We need to) Use the international break to understand why and try to avoid in the future.
"Always concerned (about defeats) but we need balance - seven wins in a row not happened then three in a row. Need the balance.
"No panic. We need to understand but no panic."