The former Juventus player believes his team will need some good fortune if if they are to stop a rampant Fernando Torres in his tracks on Tuesday night.
Torres bagged a hat-trick on Saturday in the 6-1 win over Hull, and Prandelli says: "How do you stop him? You must concentrate all the time, and be very lucky because he is so good.
"We have watched the last three Liverpool games on DVD and we know what a difficult task we face.
"Liverpool are very strong, very talented, but sometimes they are unpredictable. They are a great side, but even great sides give you opportunities."
Liverpool have won their last six on the trot in all competitions, and rattled in 18 goals in the process.
Prandelli, who became the first Fiorentina coach to take charge of 100 victories for the club when his team beat Livorno 1-0 on Saturday, has coaxed some good form from his own side so far this term.
They are fourth in Serie A and have lost just two of nine games so far, against Roma in the league and Lyon in the Champions League.
But 52-year-old Prandelli, boss of the Viola since 2005, said: "Liverpool scored six on Saturday and are in very good form, I must admit that when I heard that result it did make me a little more nervous than I was before.
"We have always said that we want to experience the Champions League with enthusiasm, even if that means running a few risks."
And there is uncertainty off the field in Florence as well as on it as they prepare to face Liverpool.
The club's president Andrea Della Valle quit last week to concentrate on his footwear business.
Della Valle still owns the club with brother Diego but has been replaced as president by Mario Cognigni.
But the upheaval has come at a bad time for the club as they face a tough European tie.
Prandelli said: "We did hear from Andrea before the Livorno match,and he is going through a tricky time. But he has not abandoned us and I believe he will be at the match against Liverpool."
Prandelli, who was a late substitute for Juventus 1-0 win against Liverpool at Heysel in the 1985 European Cup Final, faces the Anfield club for the first time since that night of horror in Brussels.
He said: "This is a different game, a different time. When I think of that final I do not think of football, now I want to forget about Heysel.
"Now I want to win this game and to bring happiness to my club and this city."
Stevan Jovetic came off the bench to convert the penalty winner against Livorno, his sixth goal in six games this term.
Fiorentina, who had Dario Dainelli sent-off in the Tuscan derby with Livorno, will be without Alberto Gilardino tomorrow.
The striker was sent off in the Italian side's 1-0 defeat away to Lyon in their opening Champions League group match earlier in the month.
Gilardino must serve a two-match ban, but midfielder Cristiano Zanetti - signed in the summer from Juventus - returns after a one-match ban.