Aguero has been sent-off three times this season - his latest for spitting at Bolton Wanderers midfielder Matty Taylor during last week's 1-0 UEFA Cup defeat.
Aguirre is convinced his young forward is paying for the way he scored his first goal for the club with his hand against Recreativo Huelva.
"This is a player who came here and dazzled everyone with his football, his goals, his age and his talent, but his misfortune is that he scored his first goal with his hand, in which he was singled out, criticized and demonized," said Aguirre. "He has not been forgiven.
"I feel that he's been tagged as a rogue player, but we must be careful with him.
"He's told me that (against Bolton) he spat at the ground, nothing else."