BVB lost 2-1 in the first-leg of the quarterfinal at the Etihad.
Hummels later said: "We still have a chance. It would have been even better if it ended 1-1, which is a fantastic result in the knockout phase.
"We know that we have to score in the return match, but we saw tonight that we created more chances, which we could not necessarily have expected.
"We must do the same in the second showdown. It will be a big challenge."