The 3-1 defeat in the first leg of their quarter-final left the European champions with the daunting task of turning the tide.
And Tuchel believes their performance at Stamford Bridge, which saw Karim Benzema score a hat-trick, effectively killed their defense of their crown.
The Chelsea manager was quick to criticize and also claimed that Romelu Lukaku’s missed header in the second half could have been the final nail in his team’s coffin.
When asked if the tie was still alive, Tuchel replied: “No, not at the moment. No.
“We have to get back to our level. I don’t know where he is since the international break. The first half is a repeat of the second half against Brentford in the quarter-final against Real Madrid. So far from our level in absolutely everything the game requires, we cannot expect a result of this kind of performance.
“I’m more worried about Southampton than Real Madrid next week. That’s my target. Today, is it alive? No, with this performance.
“If things change, maybe, but how many clubs in world football have won by three goals? How many times has this happened? So maybe we should be realistic and not get fatalistic and think I’m giving the wrong message.
“If we keep playing like this, we’ll lose at Southampton and then we’ll get hammered at the Bernabeu.”
Lukaku had a chance to cut the deficit with a second-half header – but failed to hit the target from six yards out. Tuchel admitted the miss could prove crucial.
“It was very important,” he said. “There are no more away goals, so if we’re just one goal down or a draw, then you see the momentum is back when we score.
“We could even have equalized. There were plenty of spaces and opportunities. But today’s individual decisions were nowhere near our level or our standards.
“Yes, to come back with a chance like this at 3-2, after 16 shots in the second half alone, so goals are crucial. We didn’t have them.
“We gave away a third. It’s just not possible. We can’t demand that we turn things around if that’s our foundation from this game.”