Liverpool will be without left-back Alberto Moreno for the Merseyside derby against Everton on Sunday due to an ankle injury.
The Spanish international was forced off in the first half of the Reds' 7-0 mid-week thrashing of Spartak Moscow in the Champions League, the extent of his injury sidelining him against the Toffees.
But Klopp was not able to confirm how long Moreno will be out for, with one of Andrew Robertson - who made his first appearance since September at Brighton & Hove Albion last weekend - and James Milner, first-choice left-back last season, set to replace him.
"We need to have further assessment, I cannot say much about it," the German told reporters on Moreno's injury at his pre-match press conference.
He explained that the 25-year-old's problem is "a very rare thing" and that even the specialists "aren't sure" how long he will be sidelined for so far due to "a little damage around the tendons."
Klopp insisted that Moreno will not be back for the clash with Sam Allardyce's visitors and that "if it's in a week or so or a little bit longer" the club "have to wait" to learn.
Moreno's injury is an unfortunate blow with the defender having reignited his Anfield career this season after spending last term second to Milner in his position.
But his absence - however long it may be - offers summer signing Robertson a potentially prolonged run in the starting eleven having started just four games all season, with Milner another dependable option.
Klopp refuses to confirm if 'Fab Four' will all start
Moreno and Joël Matip are Liverpool's only absentees with the centre-back struggling with a thigh injury that kept him out of the wins over Brighton and Spartak.
But despite their injuries at the back, Liverpool have the tantalising attacking quartet of Philippe Coutinho, Roberto Firmino, Sadio Mané and Mohamed Salah to choose from the start.
The four shared the Reds' seven goals against the Russian champions at Anfield on Wednesday, with Firmino having bagged a brace at Brighton and Coutinho - who scored a hat-trick against Spartak - netting a stunning free-kick on the South Coast.
Coutinho, Firmino, Mané and Salah have now shared 46 goals and 24 assists between them after 15 Premier League matches, eight Champions League outings - including the qualifiers - and one League Cup game.
Asked whether all four will start together against Everton, a tight-lipped Klopp replied: "I have nothing to say about the line-up from our side."
He insisted that he would use the rest of Friday and then even some of Saturday to "make a line-up", touching on their 'Fab Four' nickname which he feels is "disrespectful against all the other players."
"We played a fantastic game at West Ham and Alex Oxlade-Chamberlain was involved. We didn’t have Adam Lallana so far and I think he would fit fantastically in each group or band in this world," Klopp continued.
He also named Daniel Sturridge and Dominic Solanke among "all these offensive players" at Liverpool not receiving praise alongside the Reds' talismanic foursome - insisting that is "not fair."
The Reds boss continued: "It was [those four together] for the last game. [Against Everton] there will be really good offensive players if nothing happens [with injuries]. In which order or whatever, we will see, but it will be good."