The Portuguese, who spent six years at Old Trafford before his world record transfer to Spain, equalised Danny Welbeck's opener with a thumping header in the Champions League draw between the two sides.
"To play against Manchester was hard, especially for me, but I just tried to be professional and tried to do my best," Ronaldo told MUTV.
"I didn't celebrate because I played in Manchester for six years and it was very emotional for me. I just tried to do my best, to play for Madrid, to score goals, but I didn't commemorate because I think it's not fair, not respect if I commemorate."
An absorbing first leg tie ended all-square in Madrid, with the joy of Welbeck's goal offset by the frustration of further missed openings and Real's constant menace in attack.
With another enthralling 90 minutes of the tie still to come, Ronaldo feels his side are still firmly in with a chance of reaching the quarter-finals - though he is already anticipating another emotional outing on his former stomping ground. "It will be amazing to play there after four years and it will be another emotional game."
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