Castres number eight Alex Tulou is facing a spell on the sidelines after rupturing a tendon in his finger.
The powerful back-row will be out for between six to eight weeks in a blow for Christophe Urios and his side.
"Alex broke a tendon of a finger, a flexor to be exact. He had surgery on Tuesday morning and will be out six to eight weeks," Urios told Rugbyrama.
Castres hope to have Benjamin Urdapilleta and Rémi Lamerat back in action for this weekend's rescheduled Challenge Cup meeting with Pau.