The full-back played for Juve’s cross-city rivals Torino for four years between 2011 and 2015, and scored the winner in his last Turin derby appearance before joining United.
Darmian knows better than most how difficult it is to beat the Bianconeri at their own Allianz Stadium and has warned the Reds will have to be fully focused to win the return group-stage game.
“I think Juventus are a very big club, one of the biggest clubs in the world,“ he told MUTV's Mark Sullivan.
"For sure, they are the biggest club in Italy and they have won the last seven Serie A (titles) so everyone wants to beat them.