Tuchel's side knocked Real Madrid out of the Champions League last season
Chelsea boss Thomas Tuchel says his side are allowed to "dream" as they try to overturn a two-goal deficit at Real Madrid in the Champions League.
The Blues were beaten 3-1 by the Spanish side in the first leg of their quarter-final and travel to the Bernabeu for the return leg on Tuesday.
Chelsea won the competition last season under Tuchel.
"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."
Chelsea knocked Real out of the Champions League at the semi-final stage last season after a 1-1 draw in Spain - in a game played at the Alfredo Di Stefano Stadium - before following that draw up with a fine 2-0 win at Stamford Bridge.
Real have won Europe's top competition a record 13 times and no English side has ever won a Champions League game at the Bernabeu by more than a single goal.
"The task is incredibly high and the challenge is incredibly high given the circumstances of the first leg, where we play, against whom we play and at what stage we play this kind of match," added Tuchel.
"It's always allowed to dream. It is sometimes important to imagine things and to dream about it, but it will not shift the focus from the fact that we need to deliver and we need to be ready.
"We will arrive and try everything because it's worth trying. From there we see and, hopefully, we have a match where belief grows within the match by our actions and, hopefully, we can fulfil our dream, live up to our dream.
"But realistically, we have to invest a lot and be at our very top level."
- Our coverage of Chelsea is bigger and better than ever before - here's everything you need to know to make sure you never miss a momentEverything Chelsea - go straight to all the best content
Source: bbc.com