A widely circulated video clip has sparked considerable controversy regarding Atlético striker Julián Álvarez, after the Argentine appeared walking onto the pitch in the Barcelona line rather than alongside his Madrid team-mates.
The two sides met on Sunday at the "Riyadh Air Metropolitano" in matchday 12 of La Liga. Barça won it 2-1.
ESPN posted a video of both teams entering the pitch on their Facebook account, captioning it: "Julián Álvarez mistakenly found himself on the other side, and walked out onto the pitch with the Barcelona players."
Barcelona star Fermín López appeared in the same video walking out alongside the Atlético players.
Argentine outlet "Deportes 24" offered a different explanation on X. The referee, they said, had asked the players in the tunnel to mix with one another in honour of the memory of Jesús de Miguel, who died a few days earlier.
Barcelona chased Álvarez during the last summer transfer window, but Atlético refused to open negotiations with the Catalans over the deal.