The 24-year-old was injured during Sunday's 1-0 victory over Rayo Vallecano and is unlikely to feature again this season. The club confirmed that the problem involves tendon damage in the upper part of the hamstring in his right thigh.
Barrenetxea is due to undergo surgery in Madrid on Friday, November 13, with specialist Lasse Lempainen performing the operation. The Finnish surgeon also treated the winger in 2022, when a serious injury to his left hamstring kept him out for almost seven months.
The similarity between the two injuries has heightened concern at Real Sociedad. Although the affected leg is different, the prospect of another extended rehabilitation period is particularly troubling given the form Barrenetxea had produced before Sunday's setback.
He had featured in 11 of Real Sociedad's first 12 LaLiga matches, starting eight, and had also appeared in three of their four Europa League fixtures. His performances had earned him a place in Luis de la Fuente's Spain squad for the international break, although the injury forced him to withdraw.
Barrenetxea had also been influential in the team's recent results, providing two assists for Orri Óskarsson in consecutive matches against Lyon and Rayo Vallecano.
The latest came against Rayo, when his contribution helped secure the victory before he was forced off with the injury. It was a cruel interruption to a season in which he had become an important attacking presence for Matarazzo.
As reported by Mundo Deportivo, the recovery period could extend to five or six months, although the precise timetable will depend on the operation and his rehabilitation. Real Sociedad have not yet confirmed an expected return date.
The club will now have to plan for a prolonged absence from one of their most productive wide players. For Barrenetxea, the immediate priority is recovering from another serious hamstring problem, with the memory of his lengthy absence in 2022 an unwelcome reminder of what lies ahead.