The Chilean implied the Swedish referee, Jonas Eriksson, was not impartial and that he favoured the Catalans.
"We lost the game we lost against Barcelona, you are frustrated and angry. Maybe I said something but I don't think that way. I want to apologise.
"I want to clarify there was no serious accusation to the referee or to Uefa. I said the referee decided the match because he didn't give us foul against Jesus Navas and then to the penalty we had a player sent off in that moment. The referee decided the game. A lot of time he didn't give the foul.
"It's a difficult profession, he had a bad day and I didn't say that he was a bad referee.
"I felt from the beginning his criteria was not the same for both teams, I think he had a bad day - everyone can have a bad day - but I didn't say that intentionally he didn't give fouls for us or did give fouls for Barcelona. I said from the beginning it was not the same criteria. I repeat, a bad day, not dishonest."
Uefa have already indicated they will be investigating further his remarks.
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