In midweek, Roma pulled off one of the greatest comebacks in the competition's history as they edged past Barcelona on away goals, and Klopp admitted that he thought the achievement was not true when first being informed of the result at the Stadio Olimpico.
The clubs will now lock horns at the last-four stage, and Klopp has acknowledged that being able to overcome a three-goal deficit to defeat the tournament favourites was "outstanding good".
At a press conference, the 50-year-old told reporters: "They are the only team of the three I haven't played before. They played a good season having had a difficult transfer window last season, lost not only Mo [Salah] but Emerson [Palmieri].
"Until we face Roma, we'll know everything about them. I watched versus Barca, outstandingly good."
Bayern Munich will face Real Madrid in the other semi-final tie.