Left-back Moreno was forced off during the first half of Liverpool’s 7-0 Champions League win over Spartak Moscow on Wednesday and has been ruled out of this weekend’s clash with Everton.
“We need to have further assessment. I cannot say much about it. It’s a very rare thing. So far the specialists aren’t sure [how long he’ll be out for],” Klopp said on Friday.
“Not Everton, but if it’s in a week or so or a little bit longer we have to wait for that. There’s a little damage around the tendons.”
Adam Lallana could be in line to return, though, after he trained on Friday having missed Liverpool’s last three matches.
Klopp was also asked to assess the form of Mohamed Salah, Sadio Mane, Roberto Firmino and Philippe Coutinho, who have been dubbed Liverpool’s ‘Fab Four’ after their outstanding displays against Spartak, but the boss refused to confirm whether the quartet will start on Sunday.
“I have nothing to say about the line-up from our side,” he continued.
“Actually, I didn’t decide it so far. We played on Wednesday and we have to wait for sure today and maybe until tomorrow to make a line-up.”
Sam Allardyce, meanwhile, heads into his first away Premier League game as Everton’s manager able to call on the services of centre-backs Phil Jagielka and Michael Keane, but it is unclear whether Leighton Baines (ankle) is fit to return.
On the challenge of facing an in-form Liverpool team, Allardyce commented: “I’ve been involved in many derbies in my managerial career, this is two clubs clashing together with great history. Unique to the city, unique in derby terms.
“It’s about handling the pressure and atmosphere, and handling a team in the best form since Jürgen arrived. There’s no doubt we have to master that front line before we can think about getting in the right areas.
“You can’t just block two players off - it’s more than that, it’s four or five. That’s the hard bit. The runs they make, their finishing ability has increased, they don’t have to rely on one goalscorer. We have to try our best to cope with that.”