 Upon joining the club, Siqueira said that "it did not take a second to decide" to join Atlético.Siqueira made his debut in a friendly match against Numancia, on 23 July 2014, which Atlético won 1–0.He made his competitive debut in the first leg of the 2014 Supercopa de España on 19 August, a 1–1 draw away to Real Madrid in which he played 64 minutes before being replaced by fellow debutant Cristian Ansaldi.