Guardiola said: "It is not always easy to settle quick but from the beginning his impact was huge in terms of goals and many other things.
"At his age, he feels pressure without a problem. I think he has a good mentality and is an exceptional player. We have to control him and take a look at what he does."
Asked if he fears Real Madrid, he said: "No I don't fear them. But I respect them a lot. I have faced them many times. I'm not going to talk great things about them, and give you my opinion. I respect Real Madrid. And if I say I'm scared of them, I would be false."
On his criticism of the pitch at the Bernabeu, Guardiola added: "I spoke of the condition of the pitch with the best wishes in the world and it's their decision. You can believe what you want when I say that. I have to have respect.
"There's the rivalry. You want to beat them, and do well, sometimes you win and sometimes you lose. I want us to do as well as we can. Be ourselves. If we can't be, it doesn't matter. But I'm not scared of them and if they beat me - as as happened many times - we will say congratulations and wish them well."