London - Liverpool manager Jurgen Klopp said midfielder Adam Lallana is "really down" after suffering a fresh injury blow that puts his chances of a World Cup call-up by England at risk.
Lallana was introduced as a substitute just after the hour mark of Liverpool's 2-1 win at Crystal Palace on Saturday, but lasted only five minutes before pulling up with a muscle injury.
"It is not good, he is really down in the dressing room," said Klopp. "It is really difficult, whatever injury it looks like a muscle one."
Lallana has made just 13 appearances this season having missed the first four months of the campaign due to a thigh tear.
The England international had been a key player in Klopp's first two seasons in charge and worked his way back into contention for Gareth Southgate's World Cup squad.
Lallana made his first international appearance since June in England's 1-1 friendly draw against Italy on Tuesday.
"The first moment I saw him going down it looked really serious," added Klopp.
"He's our friend, our boy, our mate, our player already having a difficult season.
"Maybe one of the biggest achievements of this team is they could play a season like they have so far without Adam Lallana. That is something I would never would have thought is possible.
"We were all desperately waiting for him, he is coming step-by-step back and now it is a big, big blow for us and him."
Lallana now looks certain to at least miss both of Liverpool's Champions League quarterfinal legs against Manchester City in the next 10 days.