Milan host the Reds at San Siro stadium in their opening Champions League group tie.
Fonseca said: "The support of our fans is always important for us, as it was on Saturday (against Venezia) when we arrived at the stadium, during and after the match. The support of our fans is fundamental for us. We need to feel the love of our fans..
"I think victories always bring confidence to players and fans. It will be a different match. It is important to have won against Venezia, I think we were growing even before Saturday but victories bring confidence above all to the players.
"They are a great team, they are one of the strongest teams at the moment in Europe. They have a very strong positional game and individuality that we all know. We will have to be a defensively perfect team to win.
"In the Champions League against this type of team we cannot make mistakes: if we make one mistake they score. We will have to be a complete team in defense to then be able to attack with stability. At the moment, for me, they are one of the strongest teams in Europe."