Real director Butragueno said: "It will be a special game for Cristiano. He will go back to what was his home for a long time.
"It will be a match he will never forget. We hope he will have a great game and helps us to go through."
Butragueno added: "He is a sensational player and we are so happy to have got him at Real Madrid. He's a fundamental player."
It will be an emotional return for the former Old Trafford superstar. But Butragueno insists Ronaldo will not let his love for United affect his desire to lead Madrid into the next round.
He added: "He's an exemplary professional and I am certain he will want to give his maximum to be able to help Real Madrid - his team.
"It will be a very even match-up but, if we are at our best, we can go through."