The Catalans face the Bavarians after beating Napoli on Saturday, but the former Germany international has Bayern as clear favourites.
"Of course Barcelona have the quality to be at their best in a game," he told Sky Deutschland.
"But I think Bayern would have to make a lot of mistakes and do a lot of things badly to lose to this Barcelona.
"But, in a one-off game, things can happen.
"You do something bad and you're out.
"You can correct these things in two-legged ties."