Liverpool boss Jurgen Klopp has admitted that he is worried about Daniel Sturridge's fitness and revealed that he does not know when the striker will return to action.

The 26-year-old, who was sidelined for the majority of last season with a hip problem, has been out of action with a knee injury since early October.

Sturridge is yet to play for the Reds under Klopp - who replaced Brendan Rodgers last month - and the German is in the dark over when he will brush off his latest setback.

"I think Studge will be back soon - but soon is relative and I actually don't know," he is quoted as saying by The Mirror. "He hasn't returned as fast as we thought he would, but we cannot put pressure on him.

"All I can say is that at this moment he is training outside again after four weeks. So of course he needs time so that we can bring him back to good shape.

"Once he starts training properly, I will talk about when Daniel can play. At the moment it is like he has had another summer break. He needs to train hard before I can really talk about him playing."

He has netted twice in three Premier League appearances this season.