Lionel Messi and Dani Alves were both on target in a 2-0 first-leg victory at the Etihad Stadium, a match Aguero sat out through injury.
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"We have nothing to lose," Nasri told L'Equipe. "You have to go there with the will to attack. Barcelona are a team who like to have the ball but do not like to defend. They are not used [to it]. We have our chances.
"Bayern Munich are stronger than Barca. Defensively, Barcelona, they are not fantastic. With his speed, Kun [Aguero] will hurt them."
Barcelona were level with City until Martin Demichelis was sent off for fouling Lionel Messi in the penalty area, and the Catalans have also lost to Real Sociedad and Valencia in recent weeks.
And Nasri believes his side have nothing to fear: "We gave them more trouble when we had 10 men, rather than 11. This is how we must play at Camp Nou.
"Watch Real Sociedad. With all the respect I have for them, they are no better than us and they won 3-1 against Barcelona.
"If you play without fear or complex, you can beat them. They are like everyone else."