Andoni Iraola seems likely to miss Sunday's Basque derby after being stretchered off with a hamstring injury during Athletic Bilbao's 2-0 win against BATE Borisov.
The right-back had to be substituted in the second half of his side's Champions League victory on Wednesday, and Los Leones confirmed on their official website that the 32-year-old sustained the knock in his left leg.
Iraola is now due to undergo additional tests, the results of which will shed light into the extent of the former Spain international's layoff, although he is not expected to feature against Real Sociedad.
Athletic's injury woes ahead of their trip to San Sebastian have already been exacerbated by the absences of Xabier Etxeita and Benat Etxebarria, both of whom missed the encounter with the Belarusians.
Discussing Iraola's injury in his post-BATE pleasantries, Valverde said: "We don't know whether it's a fibrillar break, we'll have to wait and see."
