Complex sentence: He spent most of his career with Athletic Bilbao after debuting in 2009 as their youngest player in a competitive match, making over 200 appearances for the club and reaching the finals of the Copa del Rey and Europa League in 2012.
Split into simpler sentences: He spent most of his career with Athletic Bilbao, where he debuted in 2009 as their youngest player in a competitive match. He made over 200 appearances for the club, reaching the finals of the Copa del Rey and UEFA Europa League in 2012.