Pellegrini insists El Kun is now too big a name to return to the La Liga.
"I don't think that Agüero will go back to Spain. Manchester City is a great destination for the very best players, for him or for Yayá Touré. If he goes to Real Madrid, it won't be Agüero's team, it will still be Cristiano Ronaldo's team.
"Same thing with Barça, Messi's team. This is going to be Agüero's team. Over the next two years, he will fight for the Ballon d'Or," he told Marca.