Joe Gomez will miss a "significant part" of the season after undergoing knee surgery, Liverpool have confirmed.
The centre-back was injured during England training on Wednesday and returned to his club for further tests.
He had an operation to repair a tendon in his left knee on Thursday and will now being a rehabilitation programme, the Premier League champions said in a statement.
"Liverpool Football Club can confirm Joe Gomez has today undergone successful surgery to repair a tendon in his left knee," the club said.
"The centre-back sustained the injury during a training session with the England national team on Wednesday.
"The issue was isolated to Gomez’s tendon, with no damage to any other associated knee ligaments.
"The operation to correct the damage, which took place in London on Thursday morning, was a success and the 23-year-old will make a full recovery.
"Gomez will begin a rehabilitation programme with the Reds' medical team immediately, with club staff carefully monitoring his progress.
"No timescale is being placed upon his return, though the issue is likely to rule him out for a significant part of the remainder of 2020-21."
The news is a major blow to Liverpool manager Jurgen Klopp, who is experiencing something of an injury crisis with his defenders.
Virgil van Dijk is likely to miss the majority of the season after having knee ligament surgery last month, while Fabinho and Joel Matip have also been battling injuries in recent weeks.
Full-back Trent Alexander-Arnold had already withdrawn from the England squad with a calf problem that could reportedly keep him out of action for four weeks.
Liverpool, who sit third in the Premier League table after eight matches, host table-topping Leicester City on November 21 in their first game after the international break.