Villarreal remain uncertain as to when they will be able to call upon the services of Santi Cazorla.
The Spain international is currently out of action as he nurses his way back to full fitness following a back injury.
Villarreal, who have endured a difficult start to the 2009/10 campaign, are desperate to have him back in contention as soon as possible.
The 24-year-old winger has spent the past three days at a medical centre in an effort to establish the full extent of his injury, but tests have yet to produce a definitive answer.
"The treatment has had no immediate effect," Dr Luis Banos, who has been working with Cazorla, told Marca.
"We need to leave it for three or four days before we can see any results."
Banos has ruled out the need for surgery, but admits he is unable to put a timeframe on Cazorla's return to action.
"Right now it is impossible to determine a deadline," added the specialist.
"Villarreal have a special medical team and it is they who are ultimately responsible. I am sure Santi Cazorla will recover, but it is not possible to fix a date."