Speaking in his pre-Villarreal press conference, as cited by Anfield Watch's Twitter account, Klopp was asked if the tie is 'done' after Liverpool beat Unai Emery's side 2-0 at Anfield in the first leg.
"Is the job done? If I was younger I'd have been really angry with that question!" said Klopp. "Of course it's not done. We have to go there and we have to try to win, knowing Villarreal will go with all they have.
"It's a semi-final. It should be tough and that is okay. We never expected it to be easy. But we played a good game at home and we better play a good game away as well.
"If Villarreal beat us and get a result, congratulations to them, that is it.
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"Maturity and experience will be very important but it's not the most decisive thing. Everything that we are as a team is required tomorrow night. They will go for us. High press, they will spread the play. We have to be ready.
"Unai will for sure try to adapt a few things to us. It will be really interesting."
Anfield Watch Verdict
This game will not be a stroll in the park. Villarreal are going to be attacking a lot more than they did in the first leg of this tie.
With Gerard Moreno also returning from injury for Villarreal, if he starts against the Reds then Emery's side will be trying to exploit our high-line.
Luckily we've had a lot of experience with teams trying to do that this season and so far it hasn't really cost us.
Hopefully, we can see a similar result to what we saw in the first leg of this tie.