Barcelona midfielder Frenkie de Jong suffered a major ankle injury in victory over Celta Vigo.
The Dutchman is unlikely to be seen again until November.
Barca announced last night: "Tests carried out tonight have shown that the first team player De Jong suffers an injury to the distal tibioperoneal syndesmosis of the right ankle.
"He is out of the squad and his progress will determine his availability."
Barca's statement suggests De Jong is out if the ElClasico to be played on 28 October against Real Madrid at the Montjuc stadium.
