Payne has been nursing a groin injury and will be a notable absentee as the Ulstermen chase their first European win on French soil.

Paddy Jackson has shaken off an ankle complaint, but the youngster will start on the replacements bench with his out-half berth being taken by the versatile Ruan Pienaar.

Pienaar's switch from scrum half opens the way for the recently-married Paul Marshall to reclaim the number 9 jersey - he scored a brace of tries against Castres in October.

Neil McComb has forced his way into the second row alongside Lewis Stevenson, who has been called up to the Ireland training squad. It will be McComb's first Heineken Cup start after three previous appearances off the bench.

Young Ireland international Iain Henderson makes way for McComb, while Roger Wilson slots in at number 8 for knee injury victim Nick Williams.

Ulster, who lead Pool 4 by five points from Northampton Saints, have already qualified for the quarter-finals but they will want to guarantee a home draw in the last-eight by beating Castres this weekend.

With many permutations with regards home quarter-finals, centre Darren Cave believes the best thing to do is for the team to focus on winning Saturday's match and forget about results elsewhere.

"Well, the beauty of the Heineken Cup is that you can sit there with a calculator all day and worry about where you're going to be, but from my perspective this rugby team just wants to win matches," he said.

"So, a home quarter-final would be brilliant but the bottom line is that we want to win matches. We haven't won in France before in a competitive match.

"It's going to be a tough one but it's one we are looking to win. We did it at the start of the season with a pre-season win over Bayonne, so there's no reason why we can't do it again."

ULSTER (v Castres Olympique): Craig Gilroy; Andrew Trimble, Darren Cave, Paddy Wallace, Michael Allen; Ruan Pienaar, Paul Marshall; Tom Court, Rory Best, John Afoa, Lewis Stevenson, Neil McComb, Robbie Diack, Chris Henry (capt), Roger Wilson.

Replacements: Rob Herring, Callum Black, Declan Fitzpatrick, Iain Henderson, Mike McComish, Michael Heaney, Paddy Jackson, Chris Cochrane.