The Argentine legend is of the opinion that the 23-year-old would reach the next level at the Spanish capital club, adding that Los Blancos' president, Florentino Perez, has "no limits" and could bring his son-in-law to Jose Mourinho's team despite resistance from the English club.
Maradona went on to say that Aguero should have joined Madrid instead of Premier League leaders City last summer.
"Kun [Aguero] has to play for Real Madrid. If he signed for them, it would be his big break," the Al Wasl coach told Argentine radio station Radio La Red.
"Even though he is flying at City, the best thing would have been to sign for Madrid. He made a mistake.
"Now, as he is doing so well, it will be difficult to get him from City. They will want to keep him because [manager Roberto] Mancini has him very much in his plans.
"However, if Madrid want someone, they get them. Florentino has no limits. It's a question of convincing City, but not with money because they have plenty of that."
Maradona went on to theorise that Portuguese ace Cristiano Ronaldo could reach new heights if partnered with the 23-year-old.
"If Kun was playing for Madrid they would close in further on Barcelona. We would be talking about Cristiano Ronaldo scoring 60 and more goals, because Kun would move the entire defence," the 51-year-old argued.
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