The Reds boss sees a worthy adversary in his Villarreal counterpart ahead of the Champions League clash this week.

Jurgen Klopp says Liverpool cannot afford to underestimate Villarreal when they meet in the semi-finals of the Champions League this week as he hailed coach Unai Emery as "world class".

Liverpool will host the Spanish side in the first leg of the last-four tie at Anfield on Wednesday.

Having seen their opponents get the better of Juventus and Bayern Munich in the last two rounds, Villarreal have impressed Klopp with their performances and he expects a tough battle against his counterpart Emery.

We did a proper analysis. I had a lot of respect for Unai Emery and Villarreal before because I saw the games but only with one eye," Klopp said at a press conference.

"Meanwhile, I [have] now watched them properly and wow, impressive!

"Unai is obviously a detail obsessed manager who prepares for all different situations in the game and that is what his team executes.

"It’s really, really good, different ways to build up and press and react. Really impressive.

"Unai is a world class coach and is doing an incredible job there. The good thing is we are not involved in all the games.

Our job is to make life as difficult as possible for them and that is what we try to do over these two legs."

Klopp says it is difficult to predict how Villarreal will approach the game going by the way they have lined up in recent matches, as he believes Emery has a plan in place for every development.

"I can’t answer a lot about the domestic form. They are seventh in the league, and on a pretty good run of results," he added.

"After they won the quarter-final against Bayern, in between they played [Athletic Club] and Unai changed 11 times and they drew there.

"Then after that they won against Valencia, who were in the cup final.

If they played the season longer, they probably would end up in the Champions League spots but that is how it is in Spain, it is very competitive. It is a difficult league to play in and be successful in.

"Unai shows he has a plan for each result, whether you are 0-0, 1-0 up, 1-0 down, more possession, less possession.

Even if they are not winning, they are close. That is really impressive and it is a tough competition and we need exactly that, a plan for each possible result.

"First go for it, then deal with it."