Barcelona were fined 602 euros (£503) after Atletico Madrid complained about contact the club made with striker Julian Alvarez.
Complaint and sanction
Atletico accused Barcelona of approaching Julian Alvarez without first notifying them in writing. The fine was issued by the Spanish football association.
Fifa response
Atletico also complained to Fifa, but football's governing body declared it had no jurisdiction over the case.
Alvarez's position
Julian Alvarez remained at Atletico and has a contract which runs until June 2030. In an interview during the summer, Alvarez said he wanted to "fulfil his dream" of playing for Barcelona.
Apology after Saturday win
Following Atletico's victory against Deportivo La Coruna on Saturday, Alvarez apologised to Atletico's fans. He said: "It was a mistake. I understand why the fans are angry. If I were a fan, I'd be angry too. Especially given how they've supported me since I arrived."