The French midfielder says Manuel Pellegrini's men have nothing to fear as they attempt to overturn a two-goal deficit at Camp Nou.
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 because of injury.
The Argentine is back in the side for Wednesday's match, though, and given Barca's form has faltered in recent weeks, most recently in defeat at Valladolid on Saturday, Nasri is bullish about City's chances of causing an upset at Camp Nou.
"We have nothing to lose," the France international 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."
City was holding Barcelona in the first leg until Martin Demichelis was sent off for fouling Lionel Messi in the penalty area, leading Nasri to conclude that Manuel Pellegrini's men have no reason to be afraid of the task ahead of them.
"We gave them more trouble when we had 10 men, rather than 11. This is how we must play at Camp Nou," the former Arsenal ace said. "Look at Real Sociedad: With all the respect I have for them, they are no better than us and they won 3-1 against Barcelona [on February 22].
"If you play without fear or complex, you can beat them. They are like everyone else."