The BVB boss felt his side looked "vulnerable" against Dieter Hecking's men, saying they must improve considerably ahead of their all-German Champions League final on May 25
The Schwarzgelben found themselves 3-1 down with only six minutes remaining, having fallen behind in the first half, but they secured a point, and a runners-up finish in Bundesliga this season, thanks to a pair of late Marco Reus strikes.
However, their coach was critical of his side's methods during their trip to Lower Saxony and suggested they could not afford to cause themselves such problems when they face Bayern Munich in the Champions League final on May 25.
"My team have done many things of late, but unfortunately we missed the chance to zip the bag. We got away with a black eye," the 45-year-old told reporters after the match.
"We started very well, then diminished at an equal rate. We soon fell behind by a clear margin and began to look vulnerable.
"We caused ourselves problems which could have been avoided if we played better football, and I saw a lot of negative things that we shouldn't have done."