Barcelona suspect midfielder Marc Bernal suffered an anterior cruciate ligament injury in Tuesday's 2-1 win against Rayo Vallecano and could miss the majority of the season, a source told ESPN.
Bernal, 17, was forced off in the final minutes of the match in Vallecas as Barça came from behind to make it three wins from three to start the new campaign in LaLiga.
However, the injury to Bernal tainted the victory, with coach Hansi Flick saying the youngster will undergo tests on Wednesday but confirming that he fears the worst.
"It's a sad victory because Marc Bernal is injured and it looks not so good," Flick said in a news conference after the game.
"We have to wait and see how heavy it is. We win, it's OK, but when you see the dressing room nobody is happy.
"It's not good. He made a fantastic match -- 17-years-old, such a performance. It hurts."
Bernal has been one of the positives of Barça's bright start to the season, making his debut for the club in the opening day win over Valencia after impressing Flick in preseason.
Playing at the base of the midfield, the Spain youth international is one of three 17-year-olds to have started all three of the Blaugrana's league games so far, along with defender Pau Cubarsí and winger Lamine Yamal.
It creates further problems in midfield for Barça, with Frenkie de Jong and Gavi also currently sidelined with injuries and Ilkay Güngodan returning to Manchester City last week.
However, Flick insists the club are well covered in the position and will not make any panic signings with the transfer window due to close on Friday.
"This is very close to the match," he added when asked if Barça would turn to the market to cover a potential long-term injury for Bernal.
"Now we have to think about everything, but at the end of the day we have many players. We have one match more before the international break and then hopefully players coming back. We can cover the No.6 [position] no problem."
Prior to Bernal's injury, Dani Olmo celebrated a dream debut for Barça, coming off the bench to score an 82nd-minute winner after Pedri had cancelled out Unai López's opener.
The win took the Catalan side to the top of the table with nine points from a possible nine, representing their best start to a league campaign since the 2018-19 season.
They return to action on Saturday when they host Real Valladolid at the Olympic Stadium before LaLiga pauses for an international break.