Despite making an instant impact to his City career, Mancini has insisted that Aguero still needs to improve his match sharpness.
"I think he needs to recover as he only finished the Copa America three weeks ago," the boss told Sky Sports News.
"He needs another two or three weeks to be 100%, maybe. For me he's a fantastic striker, young, and he's going to be a fantastic player for us."
Aguero became City's record signing when he the club joined for £35m from Atletico Madrid in July.