Barcelona have released a statement saying that Sergi Roberto strained his hamstring in the goalless draw against Olympiakos.
Sergi Roberto, playing in midfield in Athens, was taken off just before halftime after pulling up following a foul.
The Catalan club say further tests will take place on Wednesday to determine the full extent of the injury and how long the player will be sidelined.
The statement said: “Sergio Roberto had to be substituted at the end of the first half against Olympiacos as he has a hamstring strain in his right leg.
“On Wednesday, the Barça midfielder will have more tests to find out the exact extent of the injury. The man from Reus in Catalonia injured himself when defending just before the break and was replaced by Gerard Deulofeu.”