With only four points separating Pool 4 leaders Stade Francais (13 points) and Ulster and Edinburgh who are both on nine points, the Round 5 results could go a fair distance in determining who stays in the mix for a last-eight place in the Heineken Cup.
Team News: Ulster coach Brian McLaughlin has named his starting line-up and replacements for Friday's Heineken Cup Pool 4 clash with old rivals Edinburgh.
The game, billed as Ulster's most important European encounter since 1999, will see Ulster and Edinburgh fight it out for points in Pool 4, with the aim of Heineken Cup knock-out stage qualification or qualification to the quarter-finals of the Amlin Challenge Cup.
Two changes have been made to the Ulster team from the side that gained a morale-boosting victory over Munster last time out in the Magners League.
In the backs, Darren Cave partners the fit-again Paddy Wallace in the centre, with Ian Whitten the player to lose out. Up front, former Ireland Under-20 captain David Pollock will start at openside flanker, replacing the injured Willie Faloon.
On the replacements bench, Irish international Bryan Young has been named as the additional front row replacement.
Commenting on what is a must-win game for his side, McLaughlin said: "When you're playing Edinburgh you have to realise how competitive they are, they're very aggressive around the breakdown.
"Their defence is strong, and to beat them you have to be patient, you have to hold on to the ball. The last two games have been very close, but we let them slip away, so from our point of view, we've got to play from first whistle to final whistle. We've got to take the opportunities when they arise.
"The players are all ready to go; they all love to play in the Heineken Cup.
"To have Edinburgh at home at this stage, well it's just a really huge game from that point of view. The fact that qualification is still within our grasp makes it an even bigger game, and the players know that.
"I'm very hopeful we'll get a top class performance out of them on Friday night."
Meanwhile, Edinburgh coach Rob Moffat has brought out-half Phil Godman and flanker Alan MacDonald back into the visitors' side for Friday's game. Scottish internationals Godman (hip) and MacDonald (viral infection) missed last Saturday's Magners League triumph over Cardiff.
But the pair have been drafted back into the side to replace Rory Hutton, who is not registered for the Heineken Cup, and Ross Rennie, who is rested as part of his comeback from a long-term knee injury.
Moffat said: "Every game is a must-win game for us, but we know that if are going to progress in the Heineken Cup then we need a victory at Ravenhill.
"Ulster are on the same points as us in the pool, so there is a huge amount at stake on Friday.
"There were some tight calls: we felt Dave Young did well last week and has done enough to keep Geoff Cross out.
"The scenario with the centres is very interesting as well - Nick De Luca is back on the bench and pushing for a starting spot very hard. That level of competition keeps everyone on their toes.
"Ulster have got some dangerous runners and scored two tries against us when we last played at Ravenhill. But we played with a lot of confidence against Cardiff and everybody is looking forward to this game."
Prop Young will make his first ever Heineken Cup start for Edinburgh in Belfast - the city where he was born.
ULSTER: Jamie Smith; Andrew Trimble, Darren Cave, Paddy Wallace, Simon Danielli; Ian Humphreys, Isaac Boss; Tom Court, Nigel Brady, BJ Botha, Dan Tuohy, Ed O'Donoghue, Stephen Ferris, David Pollock, Chris Henry (capt).
Replacements: Andy Kyriacou, Bryan Young, Declan Fitzpatrick, Ryan Caldwell, Thomas Anderson, Cillian Willis, Niall O'Connor, Timoci Nagusa.
EDINBURGH: Chris Paterson (capt); Jim Thompson, Ben Cairns, John Houston, Tim Visser; Phil Godman, Greig Laidlaw; Allan Jacobsen, Ross Ford, David Young, Scott MacLeod, Jim Hamilton, Scott Newlands, Alan MacDonald, Roddy Grant.
Replacements: Andrew Kelly, Kyle Traynor, Geoff Cross, Craig Hamilton, David Callam, Ross Samson, Nick De Luca, Mark Robertson.
Referee: Christophe Berdos (France) Assistant Referees: Eric Gauzins, Jean-Luc Rebollal (both France) Television Match Official: Daniel Dartigeas (France)
Match Odds (Paddy Power):Ulster to win: 2/7; Draw: 20/1; Edinburgh to win: 5/2
Pre-Match Quotes:Nigel Brady (Ulster) - "It's a must-win game for us, no matter what else happens. We must get a result in order to give ourselves a chance. We have to win and rely on Stade Francais slipping up.
"Realistically we're probably going to have to pick up a bonus point somewhere along the line, too.
"Edinburgh have turned us over twice already this season. We were pretty disappointed with the way we played over there in the European game.
"And the earlier game, in the Magners League, was one we let slip away.
"As a pack, we've been playing together for a wee while now and week on week the scrum has been improving. Playing beside each other regularly gives you more cohesion. We're tighter as an eight now.
"Now it's just a matter of keeping our heads down and continuing to improve as a pack.
"As well, we've worked very hard on the whole lineout system - the throw, the calls, the lifts, the jumps and that has been going reasonably well.
"That's a key part of my game, so it's something I have to concentrate on if I'm to keep the jersey."
Chris Paterson (Edinburgh) - "This is a whole new ball game. Of the two of us Ulster are the ones in better form, and they will have home advantage but, having won at Ravenhill already this season, we know we are capable of going there and doing it.
"And, make no mistake about it, there is still a lot to play for. For perhaps the first time I can recall since I started playing in the Heineken Cup, we are coming up to weekend number 5 and you still cannot tell with any degree of certainty just how the pool is going to finish.
"Stade Francais have put themselves in pole position with one more win than ourselves and Ulster but, so far, there is no real winner or loser in our group.
"Sometimes after just a couple of rounds sides can see they are already on the way out but this pool is finely balanced and it promises to be an exciting weekend in Paris and Belfast.
"However, we know full well that if we lose at Ravenhill we will be as good as out. Ulster are a very physical, abrasive, big and powerful team but they are also pretty quick.
"The power of their game is a real threat while they now have a settled back-line with Andrew Trimble and Simon Danielli dangerous out wide.
"Of course we have to go into the game with a positive attitude. As always in the Heineken Cup, bonus points could well have a big part to play in qualification and then there is also possible Amlin Challenge Cup quarter-final qualification in the mix this time for three Heineken Cup runners-up.
"Obviously all of us target success in the Heineken Cup as the main objective but the more European games you can play at this level is all the better."
Top Scorers - 2009/10 Heineken Cup:Ulster: Points: Ian Humphreys 48; Tries: Timoci Nagusa 2; Edinburgh: Points: Chris Paterson 18; Tries: Ben Cairns, Tim Visser 1 each
Current Form - Ulster - (Magners League): Lost 23-6 away to the Newport Gwent Dragons; Won 20-16 away to the Ospreys; Lost 16-13 at home to Edinburgh; Won 30-6 away to Connacht; Won 45-24 at home to the Scarlets; (Heineken Cup): Won 26-12 at home to Bath; Lost 17-13 away to Edinburgh; (Magners League): Won 16-14 at home to Leinster; Lost 24-10 away to Munster; Lost 25-13 at home to Glasgow Warriors; (Heineken Cup): Won 23-13 at home to Stade Francais; Lost 29-16 away to Stade Francais; (Magners League): Lost 15-3 away to Leinster; Won 15-10 at home to Munster
Edinburgh - (Magners League): Won 22-21 away to Cardiff Blues; Won 62-13 at home to Connacht; Won 16-13 away to Ulster; Lost 21-19 at home to Leinster; Lost 31-10 away to the Ospreys; (Heineken Cup): Lost 31-7 away to Stade Francais; Won 17-13 at home to Ulster; (Magners League): Won 12-7 at home to Munster; Lost 9-8 at home to the Newport Gwent Dragons; Won 17-16 away to the Scarlets; (Heineken Cup): Lost 16-9 away to Bath; Won 9-6 at home to Bath; (Magners League): Lost 25-12 away to Glasgow Warriors; Lost 22-15 at home to Glasgow Warriors; Won 21-12 at home to Cardiff Blues
Previous European Meetings: 3
Saturday, October 17, 2009 - Pool 4 - Edinburgh 17 Ulster 13, Murrayfield Friday, September 18, 1998 - Pool C - Ulster 38 Edinburgh 38, Ravenhill Sunday, November 8, 1998 - Pool C - Edinburgh 21 Ulster 23, Easter Road Stadium
Heineken Cup Records:
Ulster - 2008/09: Failed to qualify from Pool 4 2007/08: Failed to qualify from Pool 2 2006/07: Failed to qualify from Pool 5 2005/06: Failed to qualify from Pool 4 2004/05: Failed to qualify from Pool 6 2003/04: Failed to qualify from Pool 1 2002/03: Failed to qualify from Pool 6 2001/02: Failed to qualify from Pool 2 2000/01: Failed to qualify from Pool 3 1999/00: Failed to qualify from Pool 3 1998/99: Champions 1997/98: Failed to qualify from Pool B 1996/97: Failed to qualify from Pool C 1995/96: Failed to qualify from Pool B
Edinburgh - 2008/09: Failed to qualify from Pool 2 2007/08: Failed to qualify from Pool 6 2006/07: Failed to qualify from Pool 2 2005/06: Failed to qualify from Pool 6 2004/05: Failed to qualify from Pool 5 2003/04: Reached the quarter-finals 2002/03: Failed to qualify from Pool 5 2001/02: Failed to qualify from Pool 3 2000/01: Failed to qualify from Pool 1 1999/00: Failed to qualify from Pool 6 1998/99: Failed to qualify from Pool C 1996/97: Failed to qualify from Pool A