Karanka is in his third season as Mou's assistant.
He remarked: "Working with the world's best in your profession is, above all, a privilege. After starting in the national youth team, working with the young players, then suddenly making the leap to work for Real Madrid with the best coach in the world is just marvellous.
"Apart from working with him, seeing his methods and enjoying being around him, I think the most important thing, and the one that means the most to me, is getting to know Mourinho the person. In the end it is him I work with every day, I have had some great experiences and not many people really know him."