Chelsea won 3-0 in Wednesday night's Champions League tie.
"It really hurts to lose like this, as we didn't have the right spirit and hunger," captain for the night Bennacer.
“We know the Champions League is another level and we have to give more. We need to learn from this, work on what we didn't do well and lift our heads.
“We always try to give everything, games like this are all about the details. Once we conceded the second goal, it was tough and our heads dropped. We need to do better and have more belief.
“We will watch the game back and see what went wrong."