Castres have signed South African loose forward Wessel Jooste as emergency cover with both regular starters Pedrie Wannenburg and Yannick Caballero out injured.
29-year-old Jooste already has Top 14 experience with Bourgoin, where he played for seven seasons, and in England with Leicester Tigers.
Castres called on Jooste - who trained with the high-flying Top 14 outfit on Tuesday and could feature in Friday's home game against leaders Toulon - with Wannenburg out for the season and Caballero out of contention with a knee injury.
Their resources were further diminished with South African-born flanker Antonie Claassen called up to France's Six Nations squad for Saturday's game with England.
"I was in contact with Castres on Saturday and I had no hesitation in coming back to France, a country I like a lot," he said.
Castres are presently fourth in the table after 18 matches, 16 points adrift of Toulon.