Villarreal's Pablo Fornals had to be taken to hospital after fainting during training and the midfielder will miss Sunday's La Liga game against Barcelona as a result.
Fornals made an "immediate recovery" but remains under observation in hospital, it was confirmed by the club on Saturday.
The 21-year-old, who has started 13 league games this season after joining the club from Malaga in July, is reported to have been suffering from low blood sugar.
Denis Cheryshev and Nicola Sansone are also unavailable for the game against the league leaders, while Andres Fernandez remains out with a knee injury.
However, coach Javi Calleja is expected to welcome back goalkeeper Sergio Asenjo - who has not played a league game since February due to an anterior cruciate ligament injury - while Samu Castillejo and Ruben Semedo have also returned to the squad.
