12 Dec, 14:42
Prop Cian Healy is expected to miss the start of the 2014 RBS 6 Nations after undergoing surgery on his injured ankle on Wednesday.
It was confirmed yesterday that number 8 Nick Williams sustained a knee injury in the win over Glasgow last Friday night and will be on the sidelines for up to eight weeks.
Full-back Jared Payne has an ongoing groin complaint and his fitness will be monitored throughout the week.
The province has never won a Heineken Cup game in France, but did record a victory on French soil in a pre-season friendly in August with a 20-15 defeat of Bayonne.
Mark Anscombe's team will face a formidable challenge in Castres Olympique who have won three of their last four home matches in the competition.
The Ulstermen beat Castres 41-17 in their opening Heineken Cup Pool 4 game at Ravenhill in October.
ULSTER Squad (v Castres Olympique) - Backs (12): Paddy Wallace, Niall O'Connor, Ruan Pienaar, Craig Gilroy, Paddy Jackson, Chris Cochrane, Paul Marshall, Andrew Trimble, Michael Heaney, Jared Payne, Darren Cave, Michael Allen.
Forwards (14): Rory Best, Callum Black, John Afoa, Nigel Brady, Mike McComish, Lewis Stevenson, Declan Fitzpatrick, Roger Wilson, Neil McComb, Iain Henderson, Tom Court, Chris Henry, Robbie Diack, Rob Herring.