The Spain number one believes that his side face a tough test in Dortmund on Wednesday, as the shot-stopper aims to surpass his 400th victory with the club
Although the German champions haven't had the ideal start to their Bundesliga campaign, an impressive performance against Man City has highlighted that they could be a major stumbling block for any team wishing to progress from the 'group of death'.
"I seem to remember the last time we won in Germany was against Leverkusen 12 years ago," conceded Casillas, speaking to the club's official website.
"We beat them 3-2 and it was difficult. It is always hard to play in Germany. This is a very exciting, enjoyable game that world football fans will like to watch.
"It's a spectacular stadium with fans that really cheer for Borussia. We hope to get three points that I think would almost put us in the next round, and give Real Madrid the peace of mind of being in the last 16 of the Champions League.
"It won't be easy. We know that Dortmund is not doing great in the Bundesliga, but this is Europe. Playing against Real Madrid and before their fans might motivate them a lot," he said.
Casillas was slightly dismissive of celebrating his 400th win for Madrid, insisting that his focus remains on improving his game and continuing to enjoy success with the club.
"Data, numbers, statistics... The truth is that you are not aware of it today. It is not easy to say that you have 400 wins in however many games.
"I don't even keep track. I think it's the work of having sacrificed in the past and, as I have said many times, it is always wanting more, excelling and aspiring to keep adding to this club," he explained.