Ronaldo will currently be weighing up the pros and cons regarding a move to Real, and Robben added: "It's totally up to him - I think he is enjoying himself over there (at United).
"I don't think you can say football is at a higher level (in Spain) because we weren't in the last final of the Champions League like them.
"But, for me, I think Madrid is the biggest club in the world and I can understand if he wants to join them.
"It's a great league - I think you play a bit more football in Spain and I am enjoying myself there."
