Nasri, who scored in City's 2-1 shock defeat by Wigan Athletic on Sunday, felt the team "woke up after 65 minutes" in the quarter-final and termed it an overall "bad performance".
City, who also lost to Wigan in the FA Cup final in May, have little time to lament, however, as they travel to Spain with the unenviable task of overturning a 2-0 first leg deficit to reach the Champions League quarter-finals.
"The big disappointment is that it is twice now that Wigan have beaten us in the FA Cup. It is really difficult to accept," Nasri was quoted as saying by British media on Monday.
"It is like - the FA Cup, they gave it us on a plate and we refused to take it.
"At training we are going to think Barcelona and try to think positive and get a result there."
Barcelona suffered a shock 1-0 La Liga defeat at struggling Valladolid on Saturday in one of their worst performances of the season, offering hopes to Manuel Pellegrini's team.
"I think anything is possible in football," Nasri said.
"I saw them this week against Valladolid. It just shows they are human."
Nasri has twice tasted bitter comprehensive defeats at Barcelona with former club Arsenal, including a 4-1 defeat in 2010.
"It is not a good memory but at the time I thought they were better than they are today.
"We played against Messi, who was unplayable. He scored four goals against us. I hope it is not the going to be the same.
"Camp Nou is always something special. It is a special feeling to play there. It is going to be difficult but I know if we play at our level we can do something."
Nasri said there was no point City sitting back and defending against the La Liga outfit in Wednesday's game.
"Exactly the same way we finished the (Wigan) game. We have nothing to lose," the French international said of their planned approach.
"If you go there and you lose it is no more but if you get a result it will be fantastic. I think we have nothing to lose. Just attack them from the start and try to score an early goal."
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