Ronaldo will play at Old Trafford on Tuesday night for just the second time when his Juventus side takes on Manchester United in the Champions League.
The Portuguese star 118 times in 292 appearances for United.
And he won three Premier League titles, one FA Cup, two League Cups and the 2008 Champions League under Ferguson.
In May, Ferguson had emergency brain surgery but has since recovered and received a standing ovation on his return to Old Trafford in September.
Speaking in his press conference, Ronaldo was asked about coming back to his former club and sent a message to Ferguson.
“Emotional, I can remember what it was like when I was at Manchester,” he told reporters.
“I won lots of trophies here. I remember the support as well, the support was fantastic.
“Here I have many memories of victories and affection and in particular with Sir Alex Ferguson, to whom I send a big hug.
“He is a person who helped me so much.”
Juventus are top of the group over United after two wins in the competitions.
And Ronaldo is confident of making it three from three.
“It will be a difficult game. We know Manchester United have a good team. They are playing at home,” he said.
“It will be tough, but we have our weapons.
“We are Juve, so we know it is going to be tough but we have chances.
“I know if we play good, if we play the way the coach wants, I think we have a good chance to win the game.
“But we have to respect Manchester United because they are a fantastic team.
“They have an experienced coach, so I expect that Juve will win the game.”