Dembele said: "The Arsenal defenders have been making mistakes and that is a chance for us to exploit. We need to put Almunia under pressure. It won't be easy but that is our objective.
"We watched Arsenal's win over Tottenham and they looked phenomenal in attack and no one can doubt they will reach the next phase of the Champions League.
"But we need to give them problems and we go into this game with more confidence and belief after getting a draw in the first game."