"It will be difficult for both teams," UEFA.com quotes him as saying. "In the first leg we saw that both sides are here on merit and they have high quality.
"The first leg decided nothing. Our position is maybe a bit better, but no more than that. I'm not worried about us making mistakes.
"There is no such thing as a football match without mistakes. It's about performing so well that your mistakes don't matter in the larger scheme of things."
Dortmund warmed up for Tuesday's game with a 3-1 home victory over Hannover in the Bundesliga on Saturday.