Aguero and Messi have been close friends since lining up alongside each other at the Under-20 World Cup in 2005, and their families often spend time together away from football.
The Manchester City striker, who will wear his injured friend's No.10 shirt for Argentina's upcoming World Cup qualifiers, has praised the four-time Ballon d'Or winner, and says that even the current holder of the award cannot match his talents.
"Not Cristiano nor anybody else is close to Leo: he's a 10 and Cristiano is three points lower," he said with a smile, referencing the Real Madrid forward's shirt number, during an interview with TyC Sports.
"Nobody is going to reach Messi's level, but everybody has their opinion. I don't say this because he's my friend, I see him and if you are alongside him he impresses you with how quickly he takes the ball."
Messi was not named in Tata Martino's squad for the games against Ecuador and Paraguay due to the knee injury he picked up against Las Palmas in September.
And with Argentina's shirt numbers running from one to 11, the Barca man told Aguero that he should be the one to take on the No.10 jersey in his absence.
"We all know what Leo is at the top level," Aguero added. "There's nobody equal to him. He is the 10 and he said to me... I have to wear it and shut up! Wearing Messi's No.10 shirt is something special."
Aguero also hailed Pep Guardiola after it was claimed on Wednesday that the Bayern Munich coach has an agreement in place to take over at City next summer.