Aguero is expected to be fit for the big game.
And Mascherano says: "Sunday is crucial because we want to stay high in the table, and because we need to give our best in every game if we want to achieve things.
"I have spoken to him [fellow Argentine Sergio Aguero] since we were with the national team. He's a great player, with loads of talent, and very experienced despite his age. I have enjoyed playing alongside him and suffered playing against him.
"He's hard to stop. He's the kind of player that can tip the balance of a game, and I hope he doesn't do that against us. But as long as we concentrate, it won't be easy for him."