Beckham wore the number seven shirt for United before moving to Real Madrid, who have been pursuing Ronaldo following his blistering form over the last two seasons.
As a United fan, Beckham wants Ronaldo to stay but he also feels it is the right setting for him to progress even further as a player under boss Sir Alex Ferguson.
"I believe he's at the right club and a club he should stay at because as much as Real Madrid are a great team and one of the biggest clubs in the world, he's only just starting at Manchester United," Beckham said.
"He's only been there a few years. He's got a lot of people around him who will protect him. As a fan of Manchester United I hope he stays there but who knows?"
Beckham added: "It's none of my business. All I'm going to say to him is congratulations on an amazing season. I'm sure he'll be crowned world player of the year and he deserves it."