Herrera admits City will be just as formidable as Juventus, but believes an erratic United have proved they can be a match for anyone.
Jose Mourinho's side turned the last Etihad derby on its head in April when they fought back from two goals down to win 3-2.
"It's true that they are the favourites because they are in unbelievable form, but this is Manchester United and you never know what can happen," said Herrera.
"I don't like to compare situations. It's a new game, a new situation. Hopefully we can win."