Reigning Top 14 champions Castres's season hangs on the balance as they host league leaders Montpellier at Stade Pierre Antoine on Friday.
Castres hold the sixth and last play-off qualification spot - also the last guaranteed place in next season's European Cup - but with just two games remaining they are in the firing line of two teams hoping to deny them the chance to extend their campaign.
The champions have been in poor form in recent weeks, with just one win in their last four matches, leaving them only three points above Stade Français and Bordeaux-Begles - who face each other on Saturday.
Montpellier are bubbling with confidence as they head west riding the wave of the five-match winning streak. In fact, their only loss in ten games came in Clermont back in February.
Three of the those of those victories have come on the road - including an historic win in Toulouse - as Fabien Galthié's team have stormed to the top of the table playing some very attractive rugby.
Their will be a hint of revenge in their air as Montpellier's only loss at home this season came at the hands of Castres in November, so les Heraultais will be aiming to return the favour against CO outfit that are still unbeaten on home soil.
The pressure will be on Castres, who must win to keep their place in the top six. With a tricky trip to Bayonne on the menu in the last round, the defending champions are in danger of missing the play-offs entirely.
"We can honestly say that it's a last 16 knock-out clash," said Castres centre Remi Lamerat.
"But given how close the championship is, there will be many crucial matches both to make the top six and to avoid relegation."
Montpellier have lost on their last four visits to Stade Pierre Antoine with their last victory in the Tarn dating back to 2011.
Montpellier president Mohed Altrad is taking nothing for granted especially as Castres beat them in the first round of the play-offs last season.
"We're going to Castres, it's going to be very tough," he said.
"If we win we can finish first or second but if we lose then we have to probably play Racing, who could spring a surprise this year."
Castres have made six changes as Brice Dulin returns at full-back and Brice Mach starts at hooker. Max Evans replaces Marcel Garvey on the right wing.
Montpellier have made six changes to the side that won in Grenoble last week as Mamuka Gorgodze is given the week off with Paul Grant starting in the back row.
Wynand Olivier starts at inside centre and there is an all-new second row. Benoit Paillaugue is rotated with Jonathan Pelissie at scrum half.
Result in Round 12: Castres won 20-16 in Montpellier
Castres: 15 Brice Dulin, 14 Max Evans, 13 Romain Cabannes, 12 Remi Lamerat, 11 Remy Grosso, 10 Remi Tales, 9 Rory Kockott, 8
Antonie Claassen, 7 Ibrahim Diarra, 6 Jan Bornman, 5 Rodrigo Capo Ortega, 4 Richard Gray, 3 Ramiro Herrera, 2 Brice Mach, 1 Yannick Forestier.
Replacements: 16 Mathieu Bonello, 17 Saimone Taumoepeau, 18 Christophe Samson, 19 Yannick Caballero, 20 Julien Tomas, 21 Daniel Kirkpatrick, 22 Romain Teulet, 23 Mihaita Lazar.
Montpellier: 15 Pierre Berard, 14 Timoci Nagusa, 13 Robert Ebersohn, 12 Wynand Olivier, 11 Rene Ranger, 10 Francois Trinh-Duc, 9 Benoit Paillaugue, 8 Alex Tulou, 7 Paul Grant , 6 Alexandre Bias, 5 Sitaleki Timani, 4 Jim Hamilton, 3 Nicolas Mas, 2 Mickaël Ivaldi, 1 Mikheil Nariashvili
Replacements: 16 Thomas Bianchin, 17 Paea Faanunu, 18 Robins Tchale-Watchou, 19 Fred Quercy, 20 Jonathan Pelissie, 21 Anthony Tuitavake, 22 Lucas Dupont, 23 Yvan Watremez
Date: Friday, April 18
Venue: Stade Pierre Antoine, Castres
Kick-off: 20.45 local (19.45
Referee: Mathieu Raynal