 He made his senior debut in the "Segunda División B" (third tier) at the age of 16, coming on as a substitute and scoring in a match against AE Prat on 8 December 2013.In three seasons at Valencia Mestalla he played 16 games and scored two goals, and made a further eight appearances, a goal and three assists for the club's under-19 squad in the UEFA Youth League.In April 2016, Martínez agreed a three-year deal to join English club West Ham United on 1 July 2016 for a fee of around £2.4 million.