Unlike the English League, reserve teams in Spain play in the same football pyramid as their senior team rather than a separate league. However, reserves cannot play in the same division as their senior team. Therefore, Bilbao Athletic are ineligible for promotion to La Liga. Reserve teams are also no longer permitted to enter the Copa del Rey. In addition, only under-23 players, or under-25 with a professional contract, can switch between senior and reserve teams.
The team went on tour to raise funds for the Basque cause, and also played in Europe and Mexico. However, the Campeonato de Vicaya continued to be played. With their best players on tour with the Basque national team, Athletic Bilbao could only field weakened sides and, as a result, chose to enter under the name Bilbao Athletic. Despite this, they still won the championship; the club's name was derived from the two clubs that merged in 1903 to become Athletic Bilbao – Bilbao Football Club and Athletic Club.
The name was revived in 1964, when Athletic Bilbao decided to establish a reserve team with Agustín Gaínza as coach. The new Bilbao Athletic initially played in local regional leagues before winning promotion to Tercera División in 1966, under Rafa Iriondo; in 1969 they first reached Segunda División.
Bilbao Athletic returned to the third level in 1996, but the main squad continued to be nurtured with several players which had spells with the reserves.
