The Argentine only left the Spanish capital for big-spending City in the summer in a move worth around £38million.
However, speculation has linked the former Atletico Madrid ace with a move to Jose Mourinho’s side at the end of the season.
Reports suggest that Real would be willing to part with countryman Gonzalo Higuain in a potential swap deal in order to snare the 23-year-old.
And despite Aguero dismissing the speculation that he could leave City in the summer, Maradona has again talked up the possibility of a move when the transfer window re-opens in June.
"Kun (Aguero) has to play for Real Madrid," Maradona told Argentine radio station 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. However, if Madrid want someone, they get them."
The former Argentina national team coach admits Real will need to spend big in order to land his compatriot.
"(Real Madrid president) Florentino (Perez) has no limits. It's a question of convincing City - but not with money because they have plenty of that," he added.
Aguero has made an immediate impact in England following his big money move last summer, netting 24 times in 41 games in all competitions.
