Castres forwards coach Serge Milhas has been replaced by former Argentina prop Mauricio Reggiardo as they battle for Top 14 survival.
The 2013 champions are currently bottom of the Top 14, having lost a third home game of the season last weekend, against local rivals Toulouse.
They have just nine games left to save their skins, with five of those on the road, however Castres are yet to pick up a single point away from home this season.
Reggiardo, who spent ten years at the club as a player, had previously coached the club in 2007 when they were also battling relegation.
Since then he has spent time coaching the Argentina forwards under Santiago Phelan.
Reggiardo earned 50 caps for the Pumas during an eight-year international career, and he featured in two World Cups.
The rest of the Castres coaching staff, backs coach David Darricarr