Nasri has been sidelined since the end of January with a hamstring problem suffered in an FA Cup tie against Huddersfield and Wenger initially feared the France international would not be back until after the last 16 first leg meeting with the Spanish champions.
However, Nasri has recovered his fitness quicker than expected and will be in Arsenal's squad at the Emirates Stadium.
"Nasri is in the squad, the starting line-up will be decided tomorrow (Wednesday)," Wenger told reporters on Tuesday.
"He is back quicker than expected. I said 21 days and it will be only 17."
Nasri trained with his team-mates on Tuesday and his presence in the Arsenal side would be a massive boost after his superb run of form this term.
Wenger is adamant the 23-year-old is not being rushed back because of the importance of the clash with Barca, but he is yet to decide whether to start the star.
"I will take no medical risk. Everyone is adamant he is completely medically available. After that it is down to me to make the decision," Wenger added.
Wenger will also have Czech midfielder Tomas Rosicky available, but French midfielder Abou Diaby is out with a calf problem.
"Rosicky is available. He is in the squad. Diaby is out with a calf problem he did with the French national team," Wenger said.