Aguero signed for City during the 2011 summer transfer window from Atletico Madrid for £38million but Maradona is backing him to head back to the Spanish capital.
He said: "Kun is the solution for the future of Madrid, and Ronaldo, the perfect complement.
"Sergio is pure movement, while (Karim) Benzema and Pipit (Gonzalo Higuain) are two tanks who can split the defence, yes, but they collide with Ronaldo.
"One of these days it will take Cristiano ahead to one of the two. Sometimes I think we are going to have to put a traffic light there to regulate traffic between them."