The story of De Marcos in Athletic goes back to the summer of 2009 when he signed from Alavés to play, in principle at Bilbao Athletic. Caparrós, however, made him debut earlier in the rojiblanco first team as a second striker. his explosion as a lion coincided, however, with the stage of Marcelo Bielsa.
The Rosario used him as a wild card until he found his place in a midfield also composed of Iturraspe and Ander Herrera. On November 20, 2011, con Marcelino on the Sevilla bench and he, acting as a left-back, scored the winning goal at Pizjuán in one of the best Athletic matches in its history. The Asturian coach did not last much longer at the Seville club.
Valverde ended up placing him later as a right-handed winger instead of Iraola, Garitano also used him as a right-handed inside and Marcelino continues to make him play close to the wing, well in defense, well in the middle.