Athletic Bilbao B
Bilbao Athletic, officially named Athletic Club "B", is the reserve team of Athletic Bilbao, a football club based in Bilbao, in the autonomous community of Basque Country. The team will play in the Segunda División B in the 2018–19 season. Founded in 1964, the team holds home matches at the small stadium attached to the club's training facility at Lezama, or occasionally at San Mamés Stadium, with its 53,500-seat capacity, for important fixtures.
Atlético Madrid
By 1939, when La Liga had resumed, Athletic had merged with "Aviación Nacional" of Zaragoza to become "Athletic Aviación de Madrid". Aviación Nacional had been founded in 1939 by members of the Spanish Air Force. They had been promised a place in the Primera División for the 1939–40 season, only to be denied by the RFEF. As a compromise, this club merged with Athletic, whose squad had lost eight players during the Civil War. The team were awarded a place in the 1939–40 La Liga campaign only as a replacement for Real Oviedo. With the legendary Ricardo Zamora as manager, the club subsequently won their first La Liga title that season and retained the title in 1941. The most influential and charismatic player of these years was the captain Germán Gómez, who was signed from Racing de Santander in 1939. He played eight consecutive seasons for the "Rojiblancos" until the 1947–48 campaign. From his central midfield position, he formed a legendary midfield alongside Machín and Ramón Gabilondo.
In 1941, a decree issued by Francisco Franco banned teams from using foreign names and the club became "Atlético Aviacion de Madrid". In 1947, the club decided to drop the military association from its name and settled on its current name of "Club Atlético de Madrid". The same year saw Atlético beat Real Madrid 5–0 at the "Metropolitano", their biggest win over their cross-town rivals to date.