The 21-year-old was withdrawn 55 minutes into his side's 2-2 draw with Swansea City on Monday after taking a knock during a challenge with centre-back Ashley Williams.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.
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.
