The revelation of 2011 for Ros Casares, Portugal international Sonia Reis, suffered a serious knee injury in practice on Wednesday and has been lost for the season.
An MRI has shown that the 27-year-old power forward tore ligaments, which means she will require surgery and need at least six months to recover.
The timing could not be worse for Ros Casares, who signed Reis before the EuroLeague Women play-offs.
She was a key player in the club's 2-0 sweep of Bourges in the quarter-finals that qualified Ros for the Final Four for the second year in a row.
Ros Casares will take on Halcon Avenida in a Liga Femenina showdown on Sunday and then meet their Spanish rivals at the EuroLeague Women Final Four when it is staged in Ekaterinburg April 8-10.