Sneijder played for Mourinho at Inter Milan and faces his old boss when Gala meet Real in their Champions League quarterfinal.
"Mourinho is like a second father to me," the midfielder told Marca. "Mourinho 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.
"He is a very special person for me. As a Coach he is incredible, number one. 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."