Sillero signed a two-year contract extension Monday that will keep him with Athletic Bilbao until 2023. He's also joined Numancia on loan for the season.
ANALYSIS Sillero is captain of the reserve team and will head to the second division in order to get more game time at the professional level. If he does well, Sillero will have no problems earning a place in the Athletic first team as the Basque club rely on promoting youth players to be successful.