Ronaldo is quoted by The Sun declaring: "I made my decision some time ago - before the Champions League Final.
"We were competing and I didn't want to say anything because it is a very important decision. I did not want to say anything here because I wanted to be focused on Portugal - but now it is finished and I am going to say more."
Ronaldo scored United's goal in the 1-1 Champions League Final draw with Chelsea on May 21 - then missed in the shootout as United won on penalties.
But by moving to Real, Ronaldo will not only fulfil his own lifelong ambition - but also the dream of his mother Dolores, who admitted last January that she would love to see her son playing for Madrid.
"You all know what I want. I cannot say anything else. In two days you will hear from me.
"It is always difficult. It is not only one person deciding, it is many people, but it can be a very good thing for everybody."
Ronaldo slammed reports that he has refused to take calls from United boss Sir Alex Ferguson during the Euro finals.
But in a statement clearly designed to infuriate the United boss, the winger added he had "nothing to say to him" and claimed he "didn't care" if Fergie got angry.
He said: "It is not true that I didn't take calls from Ferguson. But I haven't spoken to him. I was in a very important competition and we had nothing to say to each other."
Asked if he would speak to Ferguson, Ronaldo added: "I don't know who I have to speak to. I will only say what I want and what I think.
"It's my opinion. I don't care if someone gets angry. It's my decision. It's what I want. For that I say we will see."