On 4 April 2015, during a game against Sevilla FC, Muniain suffered the first serious injury of his career, being sidelined for several months with an anterior cruciate ligament ailment to his left knee– this meant he was unable to take any part in the year's Spanish Cup or Supercopa de España finals. After suffering some setbacks in his recovery process he returned to action on 20 December, replacing Iñaki Williams for the last minutes of a 2–0 home defeat of Levante UD.