Vieira has played alongside Nasri at international level and now works closely with him at the Etihad Stadium, where he is on the coaching staff, and cannot believe Deschamps opted not to take him to Brazil.
"It's a mistake," said the former Arsenal captain. "If you want to have a chance of winning the World Cup, you have to take your best players. I think this year Samir has played fantastically well. He was one of our best players at City and played a massive part in our success.
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Nasri has picked up a negative reputation which has followed him around since he was a boy wonder in France, while his time at Arsenal ended with an acrimonious move to City, but Vieira insists that the playmaker does not deserve to be labelled a troublemaker.
He added: "I played with Samir in the national team and I am still working with him at City. We have never heard anyhing like this about him.
"I think in France sometimes they are not strong enough to deal with big personalities and he does have a strong personality. It's quite surprising because Deschamps has personality and experience."
Vieira does not believe that Nasri's exclusion will affect City negatively, though, and he knows that the challenge for them is to retain their Premier League title this time.
"It is important, if you want to make your name in the top tier, you have to try to win it back-to-back [titles]," he said. "When I was at Arsenal, with all the experience we had, we never won it back to back and it is really important if you are there to win it - bam, bam, bam - three or four times in a row. That makes a real impact.
"It is about how you deal with the success. Of course, if you win it and go to any other ground as champions, it is going to be more difficult because people want to beat you even more. Mentally we will have to be prepared for that as a football club."