Westerveld suffers bad break
The former Liverpool custodian sustained the injury in his team's UEFA Champions League defeat to Lyon in midweek.
Tests on the little finger of his left hand have revealed that he will have to undergo surgery to heal the problem as it was not a clean break.
The Dutch custodian, who now expects to be sidelined for around two or three months, expressed his disappointment and frustration at the news.
"I am very annoyed because the medical tests have diagnosed a bad break that I will need surgery for," declared the Dutchman.
"It is not a clean break, it is worse than expected because the bone is like a car after an accident.
"Wednesday was the worst day I have had in some time what with the defeat against Lyon and this injury."
Sociedad's veteran shot-stopper Alberto will replace Westerveld between the sticks during his spell on the sidelines.