Barcelona have announced Philippe Coutinho suffered a hamstring injury during Saturday's Clasico defeat to Real Madrid.
The Brazil international played the full game as Madrid prevailed 3-1 at Camp Nou, leaving Barca languishing in the bottom half of the table.
Coutinho completed 84 per cent of his passes but failed to create a chance in the game, while just one of his five shots ended up being on target.
He has started four of the five LaLiga games played so far in Ronald Koeman's reign, including scoring Barcelona's goal in the 1-1 draw with Sevilla on October 4.
However, the 28-year-old – who spent the 2019-20 season on loan at Bayern Munich, helping them secure a treble – is set for a spell on the sidelines, although Barca did not reveal how long he will be out.
"Tests on Sunday morning have revealed that Philippe Coutinho has a left biceps femoris (hamstring) injury," a short statement from the club read.
"Exactly how long that means he will be out of action depends on how the injury evolves.
Coutinho's injury is a blow ahead of a midweek trip to Turin for a crucial Champions League clash with Group G rivals Juventus.
Barca also have a European game against Dynamo Kiev, as well as meetings with Deportivo Alaves and Real Betis in the league, before the November international break.