Ferguson said he understood that family has to come first before anything else including football.
Ronaldo won three Premier League titles, two League Cups, an FA Cup and a Champions League trophy playing Ferguson before departing to Real Madrid.
Ronaldo moved to Old Trafford from his home club Sporting CP as an 18-year-old in 2003.
Ronaldo's father José Dinis Aveiro died two years later while the youngster was still coming up as a top star.
Fergoson said before Ronaldo's father's passing, he had similar experience when a young player asked for a day off following the death of his mother.
“You're beat. What can you do? I went: ‘Oh, of course, son,” Ferguson said, according to Metro.
“From that moment on, if a player came to me and said ‘I want tomorrow off' I'd say: ‘Yes – can I help you?
“In the case of Cristiano, I knew his father was ill, I knew he was in hospital and it was important for him to be there.
“It didn't matter, the football. You have to understand, some things are bigger than the football club and family is definitely one of them.
“Without question, you should never ever out the club in front of your family.”