The 21-year-old was withdrawn 55 minutes into his side's 2-2 draw with Swansea City on Monday after taking a knock during a challenge with centre-back Ashley Williams.
And Liverpool have now revealed that Coutinho will require surgery on the injury, which will keep out of action for up to six weeks.
Coutinho made a huge impact on Brendan Rodgers' team last season following his January arrival from Inter, providing seven assists and scoring three goals in 13 league appearances.
He has played a similarly key role in Liverpool's unbeaten start to the new campaign, having been handed a starting berth by Rodgers in each match.
Along with league fixtures against Southampton, Sunderland, Crystal Palace, Newcastle United and West Brom, the Brazilian will also miss the upcoming League Cup clash with Manchester United.
Liverpool sit top of the Premier League with 10 points from four games and are the only side yet to suffer defeat in the English top flight this term.
Despite the loss of Coutinho, the Merseyside club's attacking ranks will be boosted by the return of Luis Suarez from his 10-match ban for biting following Saturday's encounter with Southampton at Anfield.
