The Portugal playmaker continues to be linked with a move to Camp Nou.
"Bernardo is a great player," Aguero told Stake. "He carries the ball, he sacrifices, has quality to assist and score goals and he can play in different positions.
"It would surprise me if City let him go. He is a player who contributes a lot every season, but everything is possible.
"If he finally arrives at Barca, then he will be someone who can be key to the possession game that Xavi likes."