The German club's captain believes that they should have scored in the first leg of their quarter-final tie in Spain last week.
"We played pretty well in the first leg - we put Malaga under enormous pressure and simply should have scored a few goals," he told Bundesliga.com.
"We were certainly lacking a bit of coolness in front of goal, we'll have to be much better in that respect on Tuesday. Then we'll leave the pitch as winners."
The first leg at La Rosaleda in Malaga ended in a goalless draw.