Prandelli's team go into Wednesday's Champions League tie at Bayern Munich having taken only one point in their last five Serie A outings, making them outsiders against a team who have won their last 12 matches in all competitions.
Mutu has been provisionally suspended after the Italian Olympic Committee (CONI) said that he tested positive for the appetite suppressant drug sibutramine following the 2-1 win over Bari on January 10, the team's last victory.
"Mutu? We also missing Cristiano Zanetti and Alessandro Gamberini, who were also important players. It's no good thinking about who's missing," Prandelli told reporters.
"We have to re-find our squad's spirit," he added.
"We are taking on a very strong team and we have to play with enthusiasm and the will to show that we deserve to be here."
Bayern said they were taking nothing for granted despite the difference in the respective teams' recent form.
"Only washing machines come with guarantees," said captain Mark van Bommel. "We know we're on good form, but it can vanish very quickly."
"Fiorentina are a very good team, as they've shown in the Champions' League," added coach Louis van Gaal. "They took more points than we did in the Group Stage.
"I'll be very, very pleased with a 1-0 win."
