On 30 January 2018, after six competitive appearances with Mallorca's first team, Serrano joined Celta de Vigo B.Álex Serrano deja el Mallorca y ficha por el filial del Celta (Álex Serrano leaves Mallorca and signs for Celta's reserves); La Nueva España, 30 January 2018 (in Spanish) He went on to represent, in quick succession and still in the third tier, Salamanca CF UDS,Álex Serrano, nuevo fichaje del Salamanca CF UDS para la próxima temporada (Álex Serrano, new Salamanca CF UDS signing for the next season); El Norte de Castilla, 9 August 2019 (in Spanish) CF Talavera de la Reina and UE Cornellà.Bienvenido, Álex Serrano (Welcome, Álex Serrano); UE Cornellà, 29 January 2021 (in Spanish)
