Liverpool captain Jordan Henderson will be sidelined for at least five weeks after undergoing groin surgery, the club announced on Friday.
The England international sustained the injury during Saturday's 2-0 home defeat against Everton in the Merseyside derby.
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"Henderson has successfully had a corrective procedure carried out on the adductor injury. He will begin a rehabilitation programme immediately," Liverpool said in a statement.
The statement added: "No specific timescale is being placed upon his return; however, he is ruled out initially until after the March international break."
Henderson will miss Premier League games against Sheffield United, Chelsea, Fulham and Wolves, as well as the Champions League round of 16 second leg against RB Leipzig.
The 30-year-old becomes the latest Liverpool player to suffer a long-term injury with Virgil van Dijk, Joe Gomez and Joel Matip already ruled out for the remainder of the campaign.
Speaking in a news conference ahead of the trip to Sheffield United on Sunday, Liverpool boss Jurgen Klopp said he is confident that Henderson can return to action before the season ends.
"With so many injured players who are not available at the moment, and with most of them leaders, they are here doing their rehab and they all have to be influential," he said.
"When Hendo is back he has to play this role while doing his rehab. It is not a quick one but we all hope there is a possibility for him to play a few games this season."
Liverpool are sixth in the table with 40 points from 25 games, five points adrift of fourth-placed West Ham United.