Biarritz and Ospreys will do battle for second place in Heineken Cup Pool Five on the French West coast on Sunday.
Both sides have a mathematical chance of claiming a quarter-final berth if they win big and other results go their way. The losers' European campaign will be over.
Biarritz have made seven changes to the side that lost narrowly to Saracens last week.
French international Imanol Harinordoquy returns to start at number eight while veteran prop Sylvain Marconnet moves up from the bench to run out at tighthead.
Amongst the backs, Julien Peyrelongue takes over from Marcelo Bosch at fly-half while BenoÃ®t Baby gets the nod on the left wing ahead of Ilikena Bolakoro.
Meanwhile, Ospreys have made three changes to the starting XV that beat Treviso last week.
Shane Williams, Joe Bearman and Richard Hibbard drop to the bench while Eli Walker starts on the left wing, Jonathan Thomas is at number eight and Huw Bennett wears number two.
"There's no margin for error on Sunday," said Ospreys Director of Coaching Scott Johnson.
"We'll know by kick-off time what we are playing for, if it's a Heineken Cup place or an Amlin place, but one thing you can guarantee is that we'll be giving it everything.
"Biarritz is always a difficult place to go, any French club is the same, particularly when we're in a straight shoot-out for a qualification place. There's a little bit of history between us after that magnificent quarter-final match a couple of years ago, and I'd expect another good match. They are a damn good team, but so can we be if we get our jobs right on the day.
"It's important that we represent the region well, our fans will be looking to see that last weekend wasn't a one-off. It was good to get some tries under our belt against difficult opponents that can be bloody tough to put away. We looked sharper, more clinical, but there's plenty of room for improvement yet and no one is under any illusions that we can get anything in Biarritz if we under perform. Everyone will have to be on top of their game, play well, know their roles, and if we get that right, we'll be hopeful of extending our European season into the knockout stages. I'm sure all our fans will be behind us on that score."
Rugby Union betting odds
Biarritz Olympique: 15 Iain Balshaw, 14 Taku Ngwenya, 13 Charles Gimenez, 12 Damien Traille, 11 BenoÃ®t Baby, 10 Julien Peyrelongue, 9 Dimitri Yachvili, 8 Imanol Harinordoquy, 7 Benoit Guyot, 6 Wenceslas Lauret, 5 Manuel Carizza, 4 JÃ©rÃ´me Thion, 3 Sylvain Marconnet, 2 Arnaud Heguy, 1 Fabien Barcella.
Replacements: 16 Romain Terrain, 17 Eusebio Guinazu, 18 Francisco Gomez Kodela, 19 Pelu Taele, 20 Florian Faure, 21 Marcelo Bosch, 22 Ilikena Bolakoro, 23 Dane Haylett-Petty,
Ospreys: 15 Barry Davies, 14 Tommy Bowe, 13 Andrew Bishop, 12 Ashley Beck, 11 Eli Walker, 10 Dan Biggar, 9 Rhys Webb, 8 Jonathan Thomas, 7 Justin Tipuric, 6 Tom Smith, 5 Ian Evans, 4 Ian Gough, 3 Adam Jones, 2 Huw Bennett, 1 Paul James.
Replacements: 16 Richard Hibbard, 17 Ryan Bevington, 18 Aaron Jarvis, 19 Ryan Jones, 20 Joe Bearman, 21 Kahn Fotualii, 22 Matthew Morgan , 23 Shane Williams,
Date: Sunday, January 22
Venue: Parc des Sports Aguilera, Biarritz
Kick-off: 14.00 (13.00 GMT)
Referee: Wayne Barnes