The Manchester City great was signed by Napoli last week and Cosmi was asked if he and Scott McTominay can play in the same midfield.
And Cosmi told Radio Serie A: “As (Scott) McTominay has become what he has become, maybe De Bruyne will become a slightly more tactical player. Obviously always with the characteristics that have elected him one of the best European players.
"The guarantee is (Antonio) Conte, he is not stupid to play two attackers and lose geometry in the middle of the field. You will see that he will find the right placement."
Cosmi, however, is afraid that the Belgian midfielder will not be given enough time.
"The only qualm is that we always have this towards players who, perhaps after the first bad performance, we start to say 'But at City he played as an attacking midfielder' 'But'... No, let's leave them alone.
"They have to understand our football, it wasn't easy for Platini, for Zidane... Even McTominay at the beginning wasn't what he was after a few games. I wouldn't worry about the tactical use of this player."