The 29-year-old has stressed that the Blancos will not settle for a draw on Wednesday, while he's ready to play in whatever position his coach needs him
The Spanish champions have collected six points from their opening two games against Manchester City and Ajax, and they are determined to maintain their perfect record against the Bundesliga powerhouse.
"It will be a very difficult game. However, we have to play to win against Dortmund. We will have to be on top of our game in order to bag the full three points," Essien was quoted as saying by Marca.
Essien featured at left-back in Madrid's win over Celta Vigo at the weekend, and the former Chelsea man has insisted that he's happy to play wherever the coach needs him.
"I have to admit that it's always a bit strange [to play at left-back]. Mourinho asked me to fill in there, though, and I know I can play there.
"I am happy to play in whatever position Mourinho asks me to play. I have to work hard and make sacrifices for the team. I will continue to try and help the team to three important points."
Wednesday's Champions League match at the Signal Iduna Park kicks off at 20:45CET.