Probably Ronaldo, winger or hybrid forward position he plays needs an athletic player. Unless he plays as a Raul type center forward relying on positioning he may struggle to keep up. It would be easier for him to play as a central midfielder if he had that passing aspect of his game because the deep CM position has accommodated older players. The other problem is that Real will always have an eye for the next big thing and it won't be as loyal as say United were to Giggs, Scholes.