Cristian Romero and Dominic Solanke struck Tottenham's goals before halftime for the 2-0 win. Dortmund were down to ten men on 25 minutes after Daniel Svensson was sent off for a high challenge.
Can lamented afterwards: "We were very poor in the first half, we didn't play good football and were too soft in the duels. The second half was good and we were brave and pressed well. But we need to do this all the time, and you can't play a Champions League game like we did in the first half.
"Tottenham are a very good team and it seemed like they were always one step quicker than us in the first half. I hope it's the last time we play like that because it wasn't good. In the second half, everyone wanted the ball, but in the end it was too late and that's why we lost the game."
Dortmund defender Nico Schlotterbeck also said: "The first five minutes were okay. After that, we conceded a lot of set pieces and defended poorly at the first goal. Then we got into a bit of a rut where we lost every ball.
"With the red card, the first half was very difficult and then we conceded the second. I think we played a decent game in the second half with one man down. It was balanced, but the first half was nothing.
"With one man down, we had to move more. We did that much better in the second half. If we had scored a goal, it would have become dangerous again, but as it was, we deserved to lose."
Goalkeeper Gregor Kobel reflected: "They played with a lot of intensity, especially at the beginning. I felt that we weren't able to cope with it as well as we should have. Then the red card came, which obviously broke the game. The first half was really nothing."