Ronaldo was speaking at the premiere of his documentary movie 'Ronaldo' in London.
"With Manchester United, I have a great passion," said the Portugal forward. "I say that every time."
"It was like a dream. What [agent] Jorges Mendes did for me when I was 18 was to put me in one of the best clubs in the world with the words of Sir Alex Ferguson - it was a dream to play at Sporting and move to Manchester.
"It was great because Jorges gave me his words and Sir Alex Ferguson gave me his words. I respect the people who tell me something and it happens. This guy will be my friend, my family, with me for the rest of my life.
"It's people that I trust, that I like and people I love. When Sir Alex Ferguson said 'Cristiano - I want you to come to Manchester United, you will play 50 per cent of the games', is unbelievable - the last word was the key to signing for Manchester United."