The promising defender went under the knife after picking up a knock in a friendly versus Hamburg, and will now face an extended period on the sidelines
The promising youngster sustained torn ligaments in the anterior cruciate of his right knee in the 2-1 friendly win over Hamburg in July, and went under the knife on Tuesday.
Doctors Ramon Cugat and Ricard Pruna, who performed the operation, also discovered an associated injury to the internal meniscus, which they also corrected.
Muniesa appeared to be on his way to Ajax on a one-year loan deal when he picked up the knock, but his physical problems ended the Eredivisie champions' interest.
It is not the first time the defender has suffered a serious knee injury, after enduring a similar set-back when he was 16 years old.