The Sunday Express says sources in Spain claim that the Argentine international's record £38million transfer to City is merely a stepping stone to a future switch to the Bernabeu.
Aguero's former club Atletico Madrid repeatedly refused to sell him to their arch rivals in the Spanish capital.
But rumours in Spain suggest a secret deal has been struck between City owner Sheikh Mansour and Real president Florentino Perez.
This would allow Aguero to play for City in the short term - perhaps for just a season - before completing the move he most craves to Real.
A Spanish source said: "Aguero's dream has always been to play for Real. While he is excited about playing for City, his ultimate aim is a move to the Bernabeu.
"It could be a short stay, and there is nothing Atletico can do to stop it. A lot of people in Spain believe he will join Real at the earliest opportunity."