Biarritz v Northampton:Northampton captain Bruce Reihana has labelled Saints' mission improbable against Biarritz on Sunday as "a great opportunity".
The English Premiership's bottom club head to Estadio Anoeta in San Sebastian, home of Real Sociedad football club, for an appointment with last season's beaten finalists.
Domestic results suggests Northampton could be on the end of a hiding, having lost seven from their last nine league games.
Biarritz, meanwhile, have an additional incentive, knowing they will return to the same stadium for next month's semi-finals - they face Wasps or Leinster - by sending Saints marching home a beaten team.
But Reihana said: "This is the kind of game you play rugby for. It is a great opportunity for us, and a great way for us to move forward.
"It has been a fine line for us between winning and losing, and we've tended to go off our game plan and get a bit frantic at times.
"We just have to go back to what the coaches have told us and execute our plays. And then you never know what might happen."
Saints head coach Paul Grayson has made a handful of changes from the side beaten by Bristol last weekend.
Reihana features at outside centre, with Carlos Spencer reverting to outhalf instead of Stephen Myler, while Paul Diggin - who has scored four tries in Europe this season - starts at fullback.
Switches up front see starts for lock Matt Lord and flanker Ben Lewitt.
Biarritz have beaten Munster, Sale Sharks and Bath in previous Heineken European knockout games staged at San Sebastian, and their France international scrumhalf Dimitri Yachvili said: "The stadium is magic for us.
"Although we have now played there three times, there is still a great excitement for everyone involved.
"The supporters have been going crazy with their preparations for the big day, and we love the opportunity to play for the Basque country.
"It is an exceptional experience and we are intending to do everything we can to keep our unbeaten record."
BIARRITZ: N Brusque; P Bidabe, M Gaitan, D Traille, J Bobelet; J Peyrelongue, D Yachvili; P Balan, B August, D Avril, J Thion, D Couzinet, S Betsen, I Harinordoquy, T Lievremont. Replacements: B Noirot, B Lecouls, M Carizza, M Dridi, J Dupuy, M Bosch, S Bobo.
NORTHAMPTON: P Diggin; S Lamont, B Reihana, R Kydd, B Cohen; C Spencer, M Robinson; T Smith, D Hartley, J Brooks, M Lord, C Short, P Tupai,, B Lewitt, C Labit. Replacements: M Cortese, S Tonga'uiha, M Hopley, D Gerard, D Fox, J Howard, S Myler.
Tomorrow, San Sebastian
Kick-off - 1pm (Irish-time)
On TV - Sky Sports 3
