Athletic Club II (Primera Federación): every transfer in and out, fees paid and earned, squad market value, €2.5m spent.
| Date | Player | From | To | Fee |
|---|---|---|---|---|
| 2026-08-18 | Manex Gibelalde | Athletic Club II | Grasshopper Club Zurich | Free |
| 2026-07-24 | Oier Gastesi | Athletic Club II | Tenerife II | Free |
| 2026-07-20 | Endika Buján | Athletic Club II | Racing Ferrol | Free |
| 2026-07-17 | Iker Varela | Athletic Club II | UD Ibiza | Free |
| 2026-07-08 | Eneko Ebro | Athletic Club II | Arenas de Getxo | Free |
| 2026-07-08 | Aimar Duñabeitia | Athletic Club II | Sporting Gijón | Free |
| 2026-07-07 | Ibon Sánchez | Athletic Club II | Cádiz CF | Free |
| 2026-07-04 | Player | Athletic Club II | A.E. Kifisia | Free |
| 2026-02-02 | Ekain Azkune | Athletic Club II | Racing Ferrol | Free |
| 2026-02-01 | Efe Korkut | VfB Stuttgart | Athletic Club II | €500k |
| 2026-01-17 | Eneko Ebro | Athletic Club II | FC Cartagena | Loan |
| 2025-09-03 | Wibuala Junior Bita | Athletic Club II | Kustošija | Free |
| 2025-08-17 | Iker Alday | SD Eibar | Athletic Club II | Loan |
| 2025-08-09 | Aingeru Olabarrieta | Athletic Club II | FC Andorra | Loan |
| 2025-07-28 | Luis Bilbao | Athletic Club II | Celta Fortuna | Free |
| 2025-07-25 | Álvaro Marín | Athletic Club II | Celta Fortuna | Free |
| 2025-07-22 | Iker Varela | Athletic Club II | CD Mirandés | Loan |
| 2025-07-21 | Oier Gastesi | Athletic Club II | Arenas de Getxo | Loan |
| 2025-07-17 | Eneko Aguilar | Athletic Club II | Ponferradina | Free |
| 2025-07-11 | Ekain Azkune | Athletic Club II | SV Ried | Loan |