Spain's Mallo has been ruled out of contention for this summer's UEFA European Under-21 Championship in Israel after the RC Celta de Vigo full-back tore the anterior cruciate ligament in his left knee.
The right-sided defender – who has scored once in 104 league games for Celta – suffered the injury shortly before half-time in Wednesday's 4-0 Copa del Rey round of 16 second-leg defeat at Real Madrid CF.
Despite featuring just twice for La Rojita in U21 qualifying, Mallo's hopes of playing in the finals were raised when he was chosen to appear in November's friendly victory against Italy. That dream was dashed on Thursday, however, when club medics announced the 21-year-old would be sidelined for up to eight months.
Julen Lopetegui's side begin the defence of their European title against Russia in Jerusalem on 6 June before completing Group B with matches against Germany and the Netherlands.
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