The £27m hitman is still waiting for his first Premier League goal since joining City from Wolfsburg in January.
But Mancini said: "I believe that Dzeko is one of the top strikers in Europe.
"Sometimes for a striker incredible things happen. When you can't score you don't know why, but this is the same for all strikers.
"Now we have six league games and the FA Cup Final left and I hope he can score an important goal.
"It is difficult for him but the team comes before any player.
"I can understand what is going through a striker's mind in these moments, but it is important that he continues to work hard."