Jordi Alba has been forced off in Barcelona's Champions League clash against Borussia Dortmund after suffering a hamstring injury.
The 30-year-old went down just after the half-hour mark at Signal Iduna Park and tried to play on after receiving treatment. Around five minutes later, however, he was signalling to the bench to be substituted.
Barca coach Ernesto Valverde called on Sergi Roberto to replace the Spain international, as the absence of summer signing Junior Firpo left them without another recognised left-back in the squad.
The Catalan side later confirmed that Alaba had damaged his hamstring and will undergo scans to discover the injury's severity.
"Jordi Alba has hurt his left hamstring. Tests tomorrow will reveal the full extent of the injury," the club announced on Twitter.
Alba has been ever-present in the Barca starting XI this season, having played every minute of their four La Liga matches so far.
After their European encounter against Dortmund, Valverde's men are in action again on Saturday when they take on Granada in the Spanish top-flight.
Valverde is already without French winger Ousmane Dembele, who is also struggling with a hamstring problem, and defender Samuel Umtiti, kept out by a foot injury.
However, Tuesday's game in Germany did see Lionel Messi return to action as the club icon was brought on in the second half, just two minutes after Marco Reus missed a chance to give the hosts the lead from the penalty spot.
Messi had been kept out due to a calf injury he sustained while playing in the Copa America with Argentina in the summer.
The 32-year-old was introduced just before the hour mark and took the place of Barca's 16-year-old rising star Ansu Fati, who became the youngest player to represent the club in the Champions League.