Castres Olympique become the first side to qualify for the European Challenge Cup quarter-final after clinching a soggy 13-3 win over Leeds at Stade Pierre-Antoine on Thursday, leaving the English side at the mercy of other results.
Leeds, who finish their pool campaign with 19 tournament, could yet progress as one of the two best runners-up, but will need either Brive or Montpellier to come up short in their remaining matches against Connacht and Sale Sharks.
And Auch could also come into the mix should they record an unlikely bonus-point win over Bath at the Rec.
The Guinness Premiership strugglers needed just a point in France to reach the last eight of a European competition for the first time, but came away with nothing from a tight match.
The first half remained scoreless and it was not until almost an hour had been played that Castres finally opened the scoring, Romain Terrain landing a penalty to give the home side a 3-0 lead.
Terrain kicked another penalty five minutes later to stretch his side's lead, before Rafael Carballo crossed for the only try of the night six minutes later.
Romain Teulet successfully converted to complete an 11-minute scoring burst which brought Castres 13 points and left Leeds needing a late try of their own to secure a losing bonus point.
However, Alberto Di Bernardo's penalty was all Stuart Lancaster's men could manage as the seconds ebbed away.
The victory puts Castres through to the last eight, leaving Leeds in second place in Pool Five - and on tenterhooks.
For Castres Olympique:
Pens: Terrain 2
For Leeds Carnegie:
Pen: Di Bernardo
Castres Olympique: 15 Romain Teulet, 14 Pablo Canavosio, 13 Steve Kefu, 12 Phil Christophers, 11 Rafael Carballo, 10 Cameron McIntyre, 9 Kevin Senio, 8 Florian Faure, 7 Alexandre Bias, 6 Joe Tekori, 5 Lionel Nallet (capt), 4 Tim Barker, 3 Daniel Saayman, 2 Romain Terrain, 1 Carl Hoeft.
Replacements: 16 Akvensti Giorgadze, 17 Kees Meeuws, 18 Rodrigo Capo Ortega, 19 Lei Tomiki, 20 Sébastien Tillous Borde, 21 Anthony Lagardere, 22 Lionel Mazars.
Leeds Carnegie: 15 Jonny Hepworth, 14 Leigh Hinton, 13 Rob Vickerman, 12 Lee Blackett, 11 Tom Biggs, 10 Alberto Di Bernardo, 9 Joe Bedford (capt), 8 Rhys Oakley, 7 Martin Schusterman, 6 Danny Paul, 5 Pablo Bouza, 4 Erik Lund, 3 Tom McGee, 2 Vili Ma'asi, 1 Mike Macdonald.
Replacements: 16 James Parkes, 17 Adam Hopcroft, 18 Fosi Pala'amo, 19 Calum Clark, 20 Mike Aspinall, 21 Apo Satala, 22 Andy Tuilagi.
Referee: Carlo Damasco (Italy)