The Italian watched on as his side went down 3-1 in extra time to Guingamp in Wednesday's Coupe semi-final, and is looking for his players to bounce back.
A win will guarantee second-placed Monaco a spot in next season's UEFA Champions League, while also extending the title race for another week at least.
"The most important thing now is to raise our heads and think about the derby against Nice," Ranieri said.
"Nice are doing better right now - it will be different from the first game (when Monaco won 3-0 in December).
"The players are in good spirits. They have been working well in training. We have five matches - they will be five finals."
Ranieri's future at Monaco has come under almost constant speculation in recent weeks, but the coach shrugged aside the talk as a part of management.
"It is not possible that one defeat can change everything," he added. "And my president is very intelligent.
"It is normal to hear more about my future than about the game.
"It's like PSG, who have had a great season in Ligue 1, in the Champions League. Yet the talk is about the future of (coach Laurent) Blanc.
"This is normal - this is the world of football. This is not a problem. The problem is the next game and we must focus on that."
