But former Rangers stopper Cuellar, who spent earlier parts of his career at native clubs Calahorra, Numancia and Osasuna, believes the Portuguese's strengths would pose far less of a threat in Spain compared to in the Premier League.
“I’m not sure that [La Liga] is the best for him," he told Spanish paper AS. "He’s a world-class footballer, but Spanish football is more about tactics than here.
“The offensive phases are slower, we work in a different way. He is in the best place to make the most of his explosive power and speed.
“I would compare him with Torres, who is doing better than when he was playing for Atletico [Madrid] because he is quick and makes the most of spaces that the Premier League defenders allow him.
“Those spaces don’t exist in Spain.”
And the centre-back believes that Ronaldo's United team-mates Wayne Rooney and Carlos Tevez - also linked with a summer move to Madrid - as well as Liverpool skipper Steven Gerrard and Aston Villa livewire winger Ashley Young would have a greater chance of succeeding in Spain over Ronaldo.
“Rooney, Tevez, Gerrard and many Chelsea players would succeed [in Spain]. To my mind they would adapt better than Cristiano thanks to the way they play," he said.
"[Ashley Young] is made for Spanish football. He is very offensive and can attack from the right and from the left.
“He is quick and is a hard worker, is talented and always gives a hand to the team.”
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