On 9 January 2013, during a 0–4 Copa del Rey loss at Real Madrid (2–5 on aggregate), Mallo – who was not being challenged – suffered an anterior cruciate ligament to his left knee, going on to be sidelined for the rest of the season. He scored his first top-flight goal on 23 May 2015 in the last game of the season, opening the team's account in a 3–2 home win over RCD Espanyol.