Jurgen Klopp says he has "no idea" when striker Daniel Sturridge will be available again for Liverpool.
The England international has not played since making a substitute appearance in the 0-0 Premier League draw with Southampton on November 19 as a result of a calf injury.
Klopp hopes to have the 27-year-old striker available for the Merseyside derby against Everton on December 19 but admits he cannot put a timescale on his recovery.
"Hopefully he will be back as quick as possible - but I have no idea," Klopp told a news conference ahead of Liverpool's meeting with West Ham on Sunday.
"We don't have to think about him for West Ham or Middlesbrough... What's the game after that? Everton? Maybe then but I have no idea.
"Maybe he will go on the pitch [in Friday's training session], but that means we're starting football work on the pitch and not with the team, with the rehab coach.
"You can't force these things, it doesn't matter the quality of the player. It's not perfect with our situation with Phil [Philippe Coutinho] and Danny. He's not happy, but that's the life of a footballer."