Allegri has warned his side not to relax against a Monaco side that will try everything to qualify for the final.
Juventus hold a 2-0 advantage as they go into the second leg, but Allegri wants his men to play like they are not in control.
“We need to be fully focused for the match,” he said. “Monaco have nothing to lose and will be dangerous.
“We’ve got a small advantage after the first-leg win, but we have to play as if it’s a one-off match.
“It will be difficult, but we need to have a positive approach.”