Dani Olmo will be out for around a month after dislocating his shoulder while scoring the second goal in Barcelona's 3-1 win against Atlético Madrid on Tuesday.
Olmo, 27, fell awkwardly, unchallenged, as he turned past Jan Oblak in the 65th minute to give Barça the lead for the first time in the match.
The Spain international was substituted immediately and tests at the club's training ground on Wednesday confirmed he has dislocated his shoulder.
He will miss Barça's four remaining fixtures in 2025, which are against Real Betis, Eintracht Frankfurt, Osasuna and Villarreal.
LaLiga then pauses for a short winter break, with Barça back in action on Jan. 3 against city rivals Espanyol, when Olmo could make his comeback.
The injury comes just as Olmo was finding some form, scoring a brace in the weekend win over Alavés and then following it up with another goal against Atlético as Barça moved four points clear of Real Madrid, who play Athletic Club on Wednesday, at the top of LaLiga.
Barça are also currently without Fermín López, who would be the obvious replacement for Olmo, due to a calf injury, although there is hope he could return against either Betis or Frankfurt.
Frenkie de Jong should also be available again this weekend after missing the Atlético game with flu, but Gavi and Marc-André ter Stegen remain long-term absentees, while Ronald Araújo has been granted an indefinite break to help deal with mental health issues.
Raphinha and Pedri have both returned in recent weeks, though, and showed how important they are to Hansi Flick's team with stellar showings in the win over Atlético.
Barça, who have now won six in a row in LaLiga since losing the Clásico to Madrid, are back in league action on Saturday when they travel to Betis.