Ronaldo has not played against United since leaving in 2009 for a world-record £80million fee - but he will face his former team-mates on Wednesday night in Champions League combat at the Bernabeu.
Ronaldo is regarded as one of the greatest players on the planet, but Ferdinand hopes he will not be living up to that reputation against them.
"It's obviously going to be an emotional night for Ronaldo and a great night for him too," said Ferdinand. "But hopefully it gets too emotional for him.
"We've had a few texts, but when you get into a situation like this when you're coming up against a friend, all the texts and the conversations go to one side and you don't really speak until you actually get the game over and done with.
"He has a great rapport with the fans and there is a mutual respect between them both, which is great.
"The fans appreciated him when he was here and since he's been gone they sing his name. He came here a young boy and left a world-class player. He showed a lot of respect when he left and still does.
"We're going to have to use all of our experience, courage and ability to make sure that we stop not only Ronaldo, but the other players they have, because Real are a great team.
"They have so many other weapons. We could shut Ronaldo down for 90 minutes, but they still have players to hurt us, so we have to be compact and work hard."