Gundogan plays with Havertz and Werner for Germany and is aware of how good the pair can be at full flow.
He said: "In my opinion, Havertz is even better than (Michael) Ballack in terms of his playing ability. Ballack had a certain level of aggression in his game, and a strong mentality.
"He was a top player of the previous generation - a b*****d on the pitch, in a positive sense. Kai isn't like that."