The reigning champions have faltered in their title defence this season, but the 25-year-old goalkeeper insists that the Citizens will come back stronger next year.
Roberto Mancini's men will be looking to stall their bitter rivals' title challenge when they travel to Old Trafford on Monday night.
"We have not fallen away," Hart told The Guardian. "People will say it's a massive backwards step not winning it, but it's not that.
"We are still the side to beat, still competing with every game, still kept our respect and dignity, and we will come again. We are not a flash in the pan."
United won 3-2 at the Etihad Stadium earlier in the season.