The French playmaker received criticism from manager Roberto Mancini earlier in the campaign after producing a number of sub-par displays for the team.
Reports suggested that Nasri could even leave the Etihad in the summer, but the former Arsenal player appears to be back to his best in recent weeks and was on target as City defeated Chelsea in last month's FA Cup semi-final.
Platt admits that Nasri has not always been impressive for City, but values him highly and believes he is one of the key performers at the Etihad.
"Samir, since he has been here, has blown hot and cold," said Platt.
"When he has been hot he has been absolutely roasting, he has been a tremendous player.
"Every player can have his good games and bad games.
"Samir is an exceptional player. You don't expect anything different from him.
"Even when people have been critical of him, I don't think he has had bad games. He is a very important player for us."