The 43-year-old feels that los Blancos are one of the two best teams in Europe, alongside Bayern Munich, but he is demanding a better performance from his side at the Bernabeu
The German outfit lost 6-1 at the Veltins-Arena and there are concerns that the Bundesliga outfit could suffer further embarrassment at the Santiago Bernabeu.
However, Keller is hopeful that his players will rise to the challenge this time around, even though he feels that they are going up against one of the two best teams in Europe.
“We have a young team and this match can be a good experience process,” the Schalke boss told reporters. “We have to do better than in the home match.
“We must be more compact and not let the opponent grow. Fear is not an acceptable word in football. We are going to try to do our best.
“Maybe players with small problems or injuries will not play. I do not have many options but we will try to play with our young players.
“Real Madrid and Bayern Munich are the strongest teams in the world.
“Bayer Leverkusen played bravely against PSG in Paris and we want to do the same. We must to be realistic; Real Madrid are an amazing team and when you lose 6-1 in the first leg it is not easy to reach the quarter-finals.”
Schalke are currently sat third in the Bundesliga, 24 points off league leaders Bayern.