 Gabilondo was born in San Sebastián, Gipuzkoa.A product of Real Sociedad's youth system, he appeared sparingly for the first team in his first two seasons as a professional but went on to become an important element for the Basque club, scoring five La Liga goals in 33 games during the 2003–04 campaign.In 2006, Gabilondo moved to arch rivals Athletic Bilbao on a free transfer, producing roughly the same numbers in his first two seasons combined (59 matches and seven goals).