"I hoped it was a mistake," Vieira, who played in France's 1998 World Cup final victory over Brazil, said in an interview with ITV, for whom he will work as a pundit during the finals.
Manchester City playmaker Nasri ended the season in fine style, helping his club reclaim the Premier League title, but was overlooked when Deschamps named his provisional 30-man squad this week.
Explaining his decision, Deschamps suggested that Nasri, who was suspended for three games after Euro 2012 for swearing at a journalist, could be a disruptive figure in the dressing room.
Vieira, however, said it was a mistake to leave one of France's most creative players at home.
"If you want to have a chance, you have to take your best players," Vieira, who works with Manchester City as head of the elite development squad, said.
"I think this year Samir has played fantastically well. He was one of our best players at City.
"He did everything to go to the World Cup. He has been scoring goals, making assists. The way he has grown up is his influence on the group and the team.
"He is a positive lad, he has been working really hard and he is taking more responsibility on his shoulder. He has got personality, and a strong personality.
"We've never heard anything about him (being disruptive) at City. I think in France sometimes they're not strong enough to deal with personalities.
"That is quite surprising, because Deschamps has personality and experience."
Nasri's girlfriend Anara Atanes was less eloquent in her reaction to his World Cup snub, hurling abuse at Deschamps via Twitter on Wednesday.
Nasri, signed by City from Arsenal, said he would have to consider his international future.
"I need to take time now to think about the national team," he was quoted in The Times. "Because it's been twice that they take a World Cup away from me."
Nasri also missed the tournament in South Africa in 2010.
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