Ireland have released scrum-half Kieran Marmion from their training squad in order for him to amass game time with his provincial side Connacht.
The 23-year-old, who has been battling to make the Rugby World Cup squad alongside Conor Murray, Eoin Reddan and Isaac Boss, will face Castres.
Connacht's pre-season game will take place on Friday in Saint-Affrique, with head coach Pat Lam excited to see his team tested in the south of France.
"To get away as a squad and train in a new environment in the lead up to a competitive game is a great opportunity and a very important phase in our pre-season preparations," he told Connacht's official website on Wednesday.
"A lot of young players earned game-time last week against Grenoble and we learnt a lot about where we're at. With more players coming back in, it's great to be able to follow up straight away with what will be an even tougher task away from home against Castres.
"After six weeks of training together in Galway, we're looking forward to getting away with little interruption. We expect another tough encounter against Castres as we continue to build our game and improve on the lessons from last week. We want to give everyone some game-time and try out different combinations ahead of the Munster game and then the season kick-off in three weeks' time."