Jose Mourinho's men hold a seven-point advantage over City at the top of the table with 13 league matches remaining.
Chelsea have scored more goals (55) than any other team in the league this season, and conceded the second fewest (21).
But Nasri is unimpressed by the high-flying Londoners, who City have drawn with twice this season.
"I'm a big fan of Mourinho but I am not impressed with his team, not at all," the Frenchman told British media.
"We have played them twice, one time with 10 men, and we were better than them. Then we played them at [Stamford] Bridge, and we were better than them.
"When I have seen some of their games, I do'n’t think they are that fantastic – they are just strong and have a good striker [Diego Costa] up front.
"For me they are not special at all, and I think they are going to make some mistakes. We just have to perform, to win our games, and see what's going to happen.
"This title will be like this until the end of the season. No one will win the league 10 games before the end of the season."
Nasri believes City will be champions if they reach 90 points by season's end – but they are 38 off that mark with only 39 left to play for.
The 27-year-old said Chelsea would falter with the number of games they still have left to play.
"Two months ago we were eight points behind Chelsea and came back and went level with them," Nasri said.
"Now we are seven points behind but are not going to make big talk about it. We will just try to get as many points as possible and wait for the mistake.
"They won in the last minute against Everton, so maybe next time they will draw. We just have to win our games and see what will happen.
"The season is still long, they have the Champions League and the final of the Capital One Cup as well, so have a lot of games to play."
