Callejo had youth spells with
Santamarina and
Colón, he made the step into first-team football with Colón where he scored two goals in fifteen matches for them between 2013 and 2017; his debut came on 27 April 2013 in an
Argentine Primera División win at home to
Arsenal de Sarandí. He played twenty-one times with the club and scored nine goals, including the first of his professional career in March versus
Villa San Carlos. He scored on his Liga de Loja debut on 31 January, scoring in a 1–1 vs.
Barcelona. For the rest of 2016–17, Callejo signed for Santamarina of Primera B Nacional. He played twenty-five games and netted two goals vs.
Independiente Rivadavia and
Juventud Unida respectively. On 16 January 2018, Callejo joined
Venezuelan Primera División side
Carabobo on a contract until December 2018. However, six months later, following one goal in eight Carabobo appearances, Callejo returned to Argentina to rejoin former loan club Gimnasia y Esgrima. ==Career statistics==