Lallana was brought on 63 minutes into Saturday’s victory at Selhurst Park, but was withdrawn just five minutes later after going down clutching his thigh.
With this only his 13th senior appearance in a season hampered by two injuries, this serves as a big blow for the midfielder.
Ahead of the game, Lallana stressed how he felt “fully fit” as he set his sights on a place in the England squad for this summer’s World Cup.
But speaking after Mohamed Salah‘s late strike sealed another three points for the Reds, Klopp cast a decidedly pessimistic view of the prospects of his No. 20.
But Klopp told reporters in his post-match press conference that Lallana’s injury “looked really serious.”
“I haven’t spoken with him but I saw him. It’s absolutely bad,” he said.
“We don’t know exactly what he has, but in the first moment and then I saw him going down it looked really serious, to be honest.
“It looks like something with the muscle, we couldn’t make any further assessment so far, of course, but we will do that as quick as possible.
“He’s our friend, our boy, our mate, our player having a difficult season already.
“Maybe one of the biggest achievements of the team is that they could play a season so far like they played without Adam Lallana—I never would have thought it was possible.
“So we are all desperately waiting for him and now coming step-by-step back and now…it’s a big, big blow for us today.”
Klopp is clearly a big admirer of his former next-door neighbour, but Lallana’s inability to produce a lengthy run in the side this term has seen him fall behind drastically.
England manager Gareth Southgate holds Lallana in similarly high regard, but like Daniel Sturridge his waning fitness will surely dent his hopes of making the plane to Russia.