The former Germany international believes Pep Guardiola's are overwhelming favourites against the 14th-placed "big underdog" in the Bundesliga.
Anything other than a "masterful win" for Manchester City over Schalke in the Champions League would be a surprise to Michael Ballack.
Premier League champions City take on the Bundesliga's 14th-placed side in the first leg of their last-16 tie in Gelsenkirchen on Wednesday.
Domenico Tedesco's side have won just one of their past five matches in all competitions, while City have been victorious in 12 of their previous 13 outings.
Former Bayern Munich and Chelsea midfielder Ballack believes it is the most one-sided draw in the Champions League and is anticipating routine progression for Pep Guardiola's men.
Ballack told Omnisport: "If you look at their performance they [Schalke] are the big underdog.
"Anything but a masterful win by Man City would surprise me, but Schalke has nothing to lose. They can maybe try a tactical trick or surprise the opponent with a powerful game.
"There is not much that could make me confident that Schalke could win this match because they didn't show any strengths in the last matches.
"To be honest, I have to say that between these two opponents there is the biggest gap of all the matches."