In recent years, most of Bilbao Athletic's players have been graduates from the club's youth setup ('cantera') via the feeder team, Basconia.

[3] Despite the low expectations, they still won the championship and entered the 1939 Copa del Generalísimo, as the club itself regrouped for a return to normality.

In the 1940s, a reserve team called CD Bilbao played at regional level for a few seasons, but when they had the opportunity of promotion to the third tier, the club opted instead to send players to strengthen its more prestigious local partner Arenas de Getxo.

Bilbao Athletic dropped back down to the third level in 1996, but the main squad continued to be nurtured with several players who had spells with the reserves.

After 19 seasons in Segunda División B, Bilbao Athletic returned to the second tier after defeating Cádiz CF 3–1 on aggregate in the promotion playoffs.

[5] However, in their campaign in the Segunda they were reliant on the same group, a core squad of 20-year-olds who had never played at such a high level before, and despite battling performances in most of their games, a pattern of narrow defeats led to the team finishing bottom and being relegated back down at the first attempt.

In 2022–23, Bilbao Athletic finished bottom of their section (in which the reserves of local rivals Osasuna and Real Sociedad survived comfortably) and were relegated to the five-group Segunda Federación – the first time the team had been in the fourth tier since the 1960s, and potentially damaging for player progression at the club with a wider gap between the standards of this level and La Liga.