The Frenchman, who moved to the Etihad Stadium from Arsenal in 2011, has had an inconsistent campaign with the current Premier League title holders.
While Vieira has insisted that Nasri could have been in better form this season, he is hopeful that the midfielder will opt to stay at the club.
"Samir could have done better," Vieira told Radio Monte Carlo. "I think, he, himself, is disappointed with the level he played at for several different reasons. But in the end, he remains an important player for us.
"I see him almost daily. I think he has learned a lot this year. He has faced competition and, when he was not good enough, he has been taken off. It has been an important season for him and I am sure he will come back even stronger.
"I hope he will stay. Time will tell. It's important to build a team on the long term. Samir is a very good player, a young player and I hope he will stay with us for a long time."
Ligue 1 outfit Paris Saint-Germain have been linked with a summer swoop for the 25-year-old.