Born in Barcelona, Catalonia, Martínez began his career playing youth football for local L'Hospitalet club Penya Acció Catòlica. Martínez later joined Racing de Sants, before signing for FC Barcelona. On 19 October 1941, at the age of 16 years, 10 months and 5 days, Martínez became Barcelona's youngest ever player, starting in a 4–3 loss against Real Madrid in El Clásico at Real Madrid's Estadio Chamartín. The record still stands today, with Ansu Fati becoming the second youngest ever player only in 2019 at 16 years, 10 months and 23 days old. Martínez made six further appearances for Barcelona in the 1941–42 La Liga season, before being loaned out to Sabadell in 1942 for two years. Upon his return to Barcelona, manager Josep Samitier rejected an offer from Valencia for Martínez, before a meniscus injury halted Martínez's progression at the club.
