Mate Oier Sanjurjo has been struck down by a long-term knee injury for the second consecutive season.
The Osasuna defender was forced off during Saturday's 2-0 defeat at Athletic Bilbao and now looks set for a lengthy spell on the sidelines.
He is thought to have damaged ligaments in his right knee, although the results of medical tests have yet to be confirmed.
Initial fears suggest Oier could be sidelined for up to three months, ruling him out of a crucial stage of the season.
The 23-year-old suffered a similar problem last term, in his left knee, with the injury keeping him out for much of the second half of the campaign.
Oier will now join Javier Portillo and Ludovic Delporte in the Osasuna treatment room.