With United enjoying such dominance in recent times, Giggs can see few reasons for Ronaldo to leave when Real resume their inevitable pursuit of the Portugal winger this summer.
"He is at the best club," Giggs told The Sun.
"Cristiano has proved he is the best player in the world over the last couple of years and he has done that at United, so why leave?
"He's still a young player, still learning the game and can still improve. He can do that at United."
Real have been a distant second to Barcelona in La Liga this season and were also thrashed 5-0 by Liverpool over two legs in the Champions League last 16.
Giggs added: "Real Madrid will come back purely because of the club they are and the history they have got.
"But United are more stable."