The Spanish side won 3-1 in the first leg of their quarter-final leaving Chelsea to “dream” of a come back in the return leg on Tuesday, at Madrid.
Tuchel’s side are the defending champions of the competition.
“It is one of the biggest challenges to perform away at the Bernabeu,” said the German.
“It is even more difficult if you have to earn a certain result, if you need to win with a minimum of two goals or better or maybe a three-goal difference. That makes it almost impossible and very, very difficult, but still it is worth trying.
“We need nothing else than a fantastic script that we want to be able to overcome this.”