Samuel Umtiti missed training on Friday as Barcelona prepared for a visit from Ernesto Valverde's former side Athletic Bilbao on Saturday.
The session was open to the media for the first 15 minutes and Barça later confirmed that Umtiti has a knee problem after he wasn't spotted with his teammates.
Everything suggests the France defender will miss the game against Athletic, with Clement Lenglet set to take his place.
The club have not specified how long he will be out for and there are fears that he could be out for a while, although Ernesto Valverde suggested that won't be the case.
Umtiti is also suspeneded for next week's game against Tottenham in the Champions League after getting sent off against PSV, so Lenglet needs minutes.
The summer signing from Sevilla made his first start against Girona last week, but was sent off, serving a one-game suspension against Leganes in midweek.