De La Red still hopeful of return
"Nobody can tell me: this is what it is and this is what causes it," the 24-year-old told Spanish radio.
"I am not losing hope of playing again but there have to be enough tests so that both the doctors and myself make the right decision."
The former Spain international was running back towards the halfway line in a match against Real Union when he fell face first and lay motionless.
He regained consciousness in the dressing room but has not played since.