The Argentine attacker scored twice to help his side to a 4-0 win over Aston Villa - missing out on a hat-trick by failing to convert a penalty.
Aguero's goal tally in the English top-flight now stands at 16 in 21 games and Sagna believes the 27-year-old has shown he is one of the world's best players.
“For me he is the best player in the league, and probably one of the best players in the world," he is quoted as saying by the Daily Star.
“He is class, because he trains and enjoys football on the pitch and you can tell he gives the maximum for the team. He is very good.
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“For me he is the best I have played with. I have played with great players, but he is just class.
“He never loses the ball, even when he seems to lose it he gets it back and holds it, and manages to create space and put himself in some situations and I think he lifts the team up.
“I wouldn’t like to play against him. For me he can be the best striker in the team and the league."
City currently lie fifth in the table, 10 points behind leaders Leicester City, and Sagna is confident they still have a chance at lifting the title.
“The title race is not over. Mathematically it’s not over," he added. "This team has done it in the past, so we can do it again.”