Jurgen Klopp has confirmed that James Milner suffered a "serious" injury during Liverpool's 1-0 victory over Everton in the FA Cup third round at Anfield on Sunday.
The veteran, who started the game at left-back, only managed nine minutes of action before coming off after making a tackle.
A much-changed starting XI nonetheless saw out another home win over their local rivals, with 18-year-old Curtis Jones scoring his first goal for the club.
Reflecting on Liverpool's injuries after the game, Klopp told Sky Sports News: "Two players (Milner and Joe Gomez) started the last game and one of them got injured, so that's the situation we are in.
"That's why a lot of managers make a lot of changes; it's nothing to do with the cup, it's the timing. [Milner] has pain, that says it's serious. It's [his] muscle."
Following an extremely busy past month, during which the Reds participated in five separate competitions, Klopp now has seven players who are injured.
Among those names are regulars such as Fabinho and Joel Matip, as well as Naby Keita, Xherdan Shaqiri, Nathaniel Clyne and Dejan Lovren.