De Bruyne's Belgium meets Mbappe and France in tonight's World Cup semifinal.
De Bruyne said: “He's become a star in France but when I was playing against him for City against Monaco he'd only played 10 matches.
“He hadn't played a lot of football and to tell the truth I didn't know him. Now he's playing for a great French team and in the Champions League.
“He's a different player now, and he will be a star for the next 15 years. He's had a fantastic year and he can even improve if that's possible, so yes he will be a danger to us but we are going to try and stop him from playing."