Overall it's going to be a tough day
Four-time champions Toulouse face a winner-takes-all clash with Leicester in the final round of European Cup group matches.
Toulouse sit atop Pool Two on 18 points, with Leicester, themselves twice champions, just two points adrift after last week's dramatic 15-15 draw with Ospreys.
While Sunday's clash at Welford Road is the pick of the weekend's fixtures, Irish provinces Leinster and Munster both face testing times in their bids to join Harlequins, Ulster and French duo Toulon and Clermont in the knock-out phase.
Ten other clubs can mathematically qualify for the quarters, but realistically Leinster and Munster will be vying for the two best runners-up places with Montpellier.
Leinster, seeking an unprecedented third European title in three years, travel to Exeter in a Pool Five topped by Clermont, chasing one of the two best runners-up places.
A win is the minimum requirement for the reigning champions, while five points will probably be needed along with favourable results elsewhere.
"We still have a chance this weekend. We have a very tough game in Exeter. We'll have our work cut out for us," acknowledged Leinster scrumhalf Eoin Reddan.
"Overall it's going to be a tough day, we just have to win the game and see what happens."
Two-time champions Munster kept alive their hopes of reaching this season's quarters from Pool One with an unimpressive 26-17 win over pointless Edinburgh last weekend.
A victory for Pool One leaders Saracens over Edinburgh would see them confirmed as pool winners. Munster have to defeat Racing Metro at Thomond Park and hope that Saracens lose to Edinburgh in order to top the pool.
If both Munster and Saracens win, then Munster need results elsewhere to go in their favour if they're to emerge as one of the two best runners-up.
"It's got a feeling of those great Munster classics," said Munster scrumhalf Conor Murray.
"People are coming up to you on the street already and it's only Wednesday, telling us good luck, and that they're going to be there in numbers on the day.
"It's going to be a huge day with a huge reward at the end of it if everything goes alright so we certainly need that 16th man to drive us on."
The key game of the round for those teams not yet qualified could well be the all-French clash between Montpellier and Toulon in Pool Six.
A losing bonus point at Montpellier would be enough to secure Toulon a home quarterfinal, but a home win for Montpellier in Saturday's game would vastly change the landscape for the best runners-up places.
"We're obviously seeking a first place finish for a home quarterfinal match," said Toulon assistant coach Pierre Mignoni.
"But we know it's not a done deal because we have a tough match waiting for us in Montpellier.
"We'll do everything to prepare to win this match. We'll have to be very accurate."
Toulon's Australian centre Matt Giteau said Montpellier would be boosted by the death from cancer this week of their forwards coach Eric Bechu.
"Montpellier are now at the level of Toulouse and Clermont, and the death of their coach will give them extra motivation," Giteau said.
Friday, January 18
Connacht v Zebre
(The Sportsground - Kick-off: 20.00; 21.00 GMT)
Connacht: 15 Robbie Henshaw, 14 Tiernan O'Halloran, 13 Eoin Griffin, 12 Dave McSharry, 11 Fetu'u Vainikolo, 10 Dan Parks, 9 Kieran Marmion, 8 Andrew Browne, 7 Johnny O'Connor, 6 Mick Kearney, 5 Mike McCarthy, 4 Michael Swift, 3 Nathan White, 2 Jason Harris Wright,1 Brett Wilkinson.
Replacements:16 Ethienne Reynecke, 17 JP Cooney, 18 Ronan Loughney, 19 Dave Gannon, 20 Eoghan Grace, 21 Paul O'Donohoe, 22 Miah Nikora, 23 Danie Poolman
Zebre: 15 Tito Tebaldi, 14 Giovanbattista Venditti, 13 Roberto Quartaroli, 12 Matteo Pratichetti, 11 Ruggero Trevisan, 10 Daniel Halangahu, 9 Alberto Chillon, 8 Filippo Ferrarini, 7 Mauro Bergamasco, 6 Emiliano Caffini, 5 Josh Sole, 4 Mike Van Vuren, 3 Luca Redolfini, 2 Davide Giazzon, 1 Salvatore Perugini.
Replacements: 16 Carlo Festuccia, 17 Matias Aguero, 18 David Ryan, 19 Nicola Belardo, 20 Andrea Manici, 21 Luca Martinelli, 22 Alberto Chiesa, 23 Samuele Pace.
Referee: Pascal Gauzere (France)
Assistant referees: Jean-Luc Rebollal (France), Cyril Lafon (France)
TMO: Daniel Irazoqui (France)
Biarritz v Harlequins
(Parc des Sports Aguilera - Kick-off: 21.00, 21.00 GMT)
Biarritz: 15 Iain Balshaw, 14 Taku Ngwenya, 13 Benoît Baby, 12 Damien Traille, 11 Aled Brew, 10 Jean-Pascal Barraque, 9 Dimitri Yachvili, 8 Imanol Harinordoquy, 7 Raphael Lakafia, 6 Wenceslas Lauret, 5 Pelu Taele, 4 Thibault Dubarry, 3 Ben Broster, 2 Arnaud Heguy, 1 Fabien Barcella
Replacements: 16 Jean-Philippe Genevois, 17 Thomas Synaeghel, 18 Eugène Van Staden, 19 Erik Lund, 20 Talalelei Gray, 21 Yann Lesgourgues, 22 Julien Peyrelongue, 23 Seremaïa Burotu,
Harlequins: 15 Mike Brown, 14 Tom Williams, 13 George Lowe, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans, 9 Danny Care, 8 Tom Guest, 7 Chris Robshaw (captain), 6 Maurie Fa'asavalu, 5 George Robson, 4 Olly Kohn, 3 James Johnston, 2 Joe Gray, 1 Joe Marler.
Replacements: 16 Rob Buchanan, 17 Mark Lambert, 18 Will Collier, 19 Charlie Matthews, 20 Luke Wallace, 21 Karl Dickson, 22 Ben Botica, 23 Ollie Lindsay-Hague.
Referee: John Lacey (Ireland)
Assistant referees: Paul Haycock (Ireland), Michael Black (Ireland)
TMO: Seamus Flannery (Ireland)
Saturday, January 19
Glasgow Warriors v Northampton Saints
(Scotstoun Stadium - Kick-off: 13.35, 14.35 GMT)
Glasgow Warriors: TBC
Northampton Saints: TBC
Referee: Leighton Hodges (Wales)
Assistant referees: Gwynn Morris Wayne Davies (Wales)
TMO: Huw Lewis (Wales)
Castres v Ulster
(Stade Pierre Antoine - Kick-off: 14.35; 14.35 GMT)
Referee: Nigel Owens (Wales)
Assistant referees: Sean Brickell Jon Mason (Wales)
TMO: Derek Bevan (Wales)
Cardiff Blues v Sale Sharks
(Cardiff Arms Park - Kick-off: 15.40; 16.40 GMT)
Cardiff Blues: TBC
Sale Sharks: TBC
Referee: Peter Fitzgibbon (Ireland)
Assistant referees: Eddie Hogan-O'Connell (Ireland), Will O'Connor (Ireland)
Montpellier v Toulon
(Stade Yves du Manoir - Kick-off: 16.40; 16.40 GMT)
Referee: Alain Rolland (Ireland)
Assistant referees: Stuart Gaffikin (Ireland), Kevin Beggs (Ireland)
TMO: Marshall Kilgore (Ireland)
Exeter Chiefs v Leinster
(Sandy Park Stadium - Kick-off: 18.00; 19.00 GMT)
Exeter Chiefs: TBC
Referee: Romain Poite (France)
Assistant referees: Christophe Berdos (France), Eric Soulan (France)
TMO: Bernard Dal Maso (France)
Scarlets v Clermont Auvergne
(Parc y Scarlets - Kick-off: 18.00; 19.00 GMT)
Clermont Auvergne: TBC
Referee: Neil Paterson (Scotland)
Assistant referees: David Changleng (Scotland), Adrian Graves (Scotland)
TMO: Jim Yuille (Scotland)
Sunday, January 20
Munster v Racing Metro
(Thomond Park - Kick-off: 12.45; 13.45)
Racing Metro: TBC
Referee: Wayne Barnes (England)
Assistant referees: JP Doyle, (England) Robin Goodliffe (England)
TMO: David Grashoff (England)
Saracens v Edinburgh
(Vicarage Road - Kick-off: 12.45; 13.45)
Referee: Jérôme Garces (France)
Assistant referees: Sébastien Cloute (France), Jérôme Lamirand (France)
TMO: Jean-Marie Piraveau (France)
Leicester Tigers v Toulouse
(Welford Road - Kick-off: 15.00; 16.00 GMT)
Leicester Tigers: TBC
Referee: George Clancy (Ireland)
Assistant referees: Mark Patton (Ireland), Olly Hodges (Ireland)
TMO: Simon McDowell (Ireland)
Treviso v Ospreys
(Stadio Comunale di Monigo - Kick-off: 16.00; 16.00 GMT)
Referee: Greg Garner (England)
Assistant referees: Luke Pearce (England), Paul Dix (England)
TMO: Trevor Fisher (England)