The defender thinks that the side must up their game if they want to beat Jose Mourinho's men, though Mainz goalkeeper Julian Baumgartlinger believes BVB can reach the final
The German giants host Mourinho's men on Wednesday off the back of an unconvincing victory over Mainz at the weekend and, speaking to Bild, Hummels believes Real boast the personnel in their ranks to punish the errors which did not prove costly during Saturday's win.
"If we play like this against Real Madrid, we will concede a lot of goals," he said.
However, Mainz goalkeeper Julian Baumgartlinger was much more complimentary towards Jurgen Klopp's men and believes that BVB could be destined to play in the Wembley final of the European competition this season.
"Today I felt as though Dortmund had an extra man on the pitch," the 25-year-old said. "I believe they can do anything, even winning the Champions League final."
Dortmund host Jose Mourinho's men at Signal Iduna Park on Wednesday with Barcelona's trip to Bayern Munich to be played on Tuesday night - the victors of those ties will face in London on May 25.