The Barcelona star made no secret of his admiration for Aguero's abilities when speaking to Barcelona's official website and believes that the Manchester City striker is up there with the very best.
He said: "He's a player I know very well I've known him since he was a little kid. I'm very fond of him.
"Aguero is one of the best players in the world inside the box due to his finishing and his all-round quality".
Mascherano was also full of praise for Man City manager Pep Guardiola, who had had a "massive impact" on his life.
"Guardiola has had a massive impact on my life," the Argentinian added.
"Firstly, because he brought me to this club, and secondly, because he taught me so much during the two years we were together.
"Guardiola is so influential because of his impressive reading of the game. He made a lot of things about the game very clear to me".
The former Liverpool man will go up against Aguero and Guardiola in Barcelona's Champions League group stage tie on Wednesday night.