 On 7 January 2018, Martínez made his full West Ham debut in an FA Cup third round tie at Shrewsbury Town, replacing Javier Hernández after 71 minutes in a 0–0 draw.On 1 February, he made a deadline day loan switch to Spanish Segunda División club Real Valladolid for the remainder of the 2017–18 season.He contributed with one goal in ten appearances, as his side achieved promotion to La Liga in the play-offs.