West Ham, who sold key midfielder Declan Rice (22) in the summer, travel to Anfield on Sunday having started the season in fine form, winning three out of five matches to sit sixth in the standings on 10 points.
Liverpool are three points ahead in third, but Klopp warned his side not to be complacent against the team managed by veteran boss David Moyes (60).
"There are so many extremely strong opponents, West Ham is one of them," Klopp told a press conference. "I'm happy for David (Moyes) that he really built this team now over a few years. Even with Declan Rice out, they look really good.
"With all the other guys they had already, it looks really solid and that makes it really tricky. It means for us we have to be the best version of ourselves," he added.
The German also clarified his comments on kickoff times, saying the earlier ones were not ideal for achieving peak performance.
"It's not a problem to play Thursday to Sunday. It would be better if we played a bit later, but people misunderstand when you talk about 12:30pm (on a Saturday)," he said.
"It's only two-and-a-half hours before the 3pm games, that's true, but it's completely different when you have a pre-match meal at 9am."
Klopp had expressed his frustration last week after being handed an early fixture against Wolverhampton Wanderers following the international break. Their kic-koff on Sunday is at 2pm local time.
"You can't get the guys up at five o'clock in the morning to be 100% ready for the game. All these things are very difficult," he added.
Liverpool, who were 3-1 winners of LASK in the Europa League on Thursday, will have Virgil van Dijk (32) back in defence in the league after the Dutchman missed the last two domestic games through suspension.