The Schalke boss is hoping for a minor miracle as his side takes on Carlo Ancelotti's men but believes it can take advantage of Madrid's wretched run in Germany.
Keller's side face the Blancos in the last 16 of the Champions League and will be hoping to take advantage of Madrid's woeful record in Germany where it has only won once in its last 25 attempts.
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“Behind Bayern Munich, Real Madrid is maybe the second best team in the world at this moment,” the coach told reporters. “They have extraordinary players in each position and that is why it will not be an easy game for us.
"We'll have to be compact at the back to achieve what might be a minor miracle of getting a result.
“But we are the home team and want to play in a brave way without hiding from Real. To be successful tomorrow everybody has to play at 100 percent. Then it might be possible to achieve a little wonder.”