The Brazilian came on as a second half substitute during Barca's frustrating 1-1 draw with Eibar, but was unable to finish the match after feeling discomfort in his knee and was subsequently withdrawn.
Barca have now confirmed that Coutinho has suffered damage to his lateral meniscus and the full the extent of the problem has been revealed, with the Brazilian set to miss a huge chunk of Barcelona's season.
It's another blow in the Barca career of Coutinho, whose gigantic transfer from Liverpool has proven to be a monumental disaster so far.
After failing to impress in his debut season he was sent out on loan to Bayern Munich, but back at Camp Nou this season he has often been the weak link in the side, leading to suggestions that he could soon leave the club.
But this latest injury impacts Ronald Koeman's already thin squad.
Ansu Fati is not expected to return until March following a knee problem of his own, while Gerard Pique will not play again this season, again with a serious knee issue.