Real Madrid have revealed that Spain international Ruben de la Red is suffering from a heart problem.
The midfielder collapsed on the field during Madrid's Copa del Rey clash at Real Union on 30th October and spent the night in hospital.
De la Red is still to return to action as club doctors continue to assess his condition, but president Ramon Calderon admitted that a problem with his heart had caused him to collapse.
He told radio station Cadena SER: "De la Red suffered a heart problem.
"All of the tests that have been done haven't detected anything abnormal."
Calderon added that the 23-year-old would not play again until the medical staff were certain his health was not under threat.