Joselu left Real for Qatar after helping them win the LaLiga and Champions League Double last season.
He told AS: "I know what Madrid is like and I know the qualities that Mbappé has, and for me there is no doubt. Mbappé is like a bottle of ketchup. At first you press it and it doesn't come out, but then it all comes out at once.
"He has already scored two goals against Betis and he will continue to score. Mbappé will make history at Madrid, he and all those around him.
"I have already said that Madrid is the best team in the world, but not only in terms of sport. Also in everything else, in the way players and their families are treated, in the details and in the day to day. I will always be grateful to Madrid, which is also the team of my heart.
"Wearing the white shirt has its greatness and carries its responsibility. The current Madrid not only has the best team, but also the best president (Florentino Perez)."