Massimiliano Allegri believes Juventus must be positive at Camp Nou when they begin their Champions League campaign against familiar foes Barcelona.

The Italian champions knocked out their Spanish hosts at the quarter-final stage last season on their way to the final, where they were beaten 4-1 by Real Madrid in Cardiff.

Juventus kept back-to-back clean sheets against Luis Enrique's side in the last-eight tie, yet Allegri feels his team will need to score to get something out of their Group D opener on Tuesday. 

"We're not yet in peak condition. The aim, as always, is to be fighting on all fronts come March," he told a news conference.

"Tomorrow we need to score, as to keep a third consecutive clean sheet against Barcelona would be tough.

"We need to play with great enthusiasm and passion as we bid to reach the knockout rounds."