The defender is reluctant to concede the Bundesliga title, but admits it is going to be difficult to claw back an 11-point gap between his side and leaders Bayern MunichMats Hummels was left rueing Borussia Dortmund's failure to convert a number of chances as the reigning champions were held to a 0-0 draw by Stuttgart.
BVB hit the woodwork on two occasions, with the defender himself and Robert Lewandowski the guilty men as Jurgen Klopp's side fell 11 points adrift of Bayern Munich.
"We were unlucky," Hummels told Goal.com. "We knew how important this match was to close the gap at the top of the table.
"We had a number of chances, but failed to score which was the problem, plus I had some bad luck when I hit the crossbar. If we want the three points, we have to score a goal."
The last four encounters between the two sides have ended in draws, and the German international is already looking ahead to the return fixture.
"We must make sure we win the game at Stuttgart if we are going to challenge for the title."