Mourinho's Real Madrid host the Turkish side in their Champions League quarter-final first-leg tie on Wednesday, and Sneijder has revealed the influence the Portuguese coach has had on his career ahead of the game.
"Mourinho is like a second father to me, he is a special person to me," the Dutchman told Marca.
"He is a powerhouse. In football we have powerhouses who are players, and ever since I met Mourinho, we can say that there are powerhouses who are coaches. And he certainly is, without any doubt at all.
"As a coach he is incredible, No.1. It was he who gave me confidence, and I enjoyed playing football like never before. And as a person he reaches you much more than in his role as coach. Mourinho is a friend.
"It's not easy to explain. You have to be with him to find out just what he is like. The key to him is how he convinces you, how he helps you if things aren't going well for you."
Sneijder played under Mourinho for Inter Milan.