Tevez once again has a question mark hanging over his future despite City boss Roberto Mancini declaring he was optimistic the striker would remain at Eastlands.
Johnson, currently preparing for England's Euro 2012 qualifier with Switzerland on Saturday, said: "Carlos carries us sometimes with his goals and his drive. Personally he is probably the best player I have played with.
"Some of the goals, and some of the stuff he does in training, is just unbelievable. Personally I hope we keep hold of him just like all the City fans do.
"He will be a major part next season when we are playing in the Champions League. He would be hard to replace. There are probably only five or six strikers out there who get you that many goals a season at the highest level. We have one of them, so it would be great if we could keep him."