Toulouse and Biarritz Olympique are through to the Heineken Cup quarter-finals but elsewhere the remaining six places are up for grabs - along with the three runners-up spots qualifying teams for the Amlin Challenge Cup knock-out stages.
The two French giants have done it with a match in hand but with priceless home quarter-final advantage still on offer they have every incentive in their Round 6 matches at Sale Sharks and home to Glasgow Warriors respectively.
But while there are numerous potentially thunderous do-or-die encounters in Round 6 next weekend - perhaps headlined by Northampton Saints' Pool 1 trip to face Munster at Thomond Park and defending champions Leinster's Pool 6 contest with London Irish at Twickenham Stadium - another thriller is on the cards when the Ospreys welcome Leicester Tigers to the Liberty Stadium in their on-going Anglo-Welsh tournament rivalry.
And the Ospreys have issued a rallying call to their supporters ahead of the Saturday lunchtime showdown with captain Ryan Jones challenging their Welsh fans to match their French opposite numbers from ASM Clermont Auvergne who gave their team such magnificent vocal support.
"You are talking about a fantastic arena in which to play rugby," said the Wales captain. "It was colourful, it was loud and at times intimidating and I hope our fans can do the same this weekend.
"That's the environment every team in Europe is looking to create for every game.
"If we could create that at home we would be going some way to becoming one of the great teams in Europe. It's the old 16th man - but it helps when you are winning.
"The game was in the balance but we let it go away from us and went down 27-7. There was a lack of discipline but Clermont's kicking game was superb. They punished us in open play and from some of the penalties we conceded...we came off second best."
And Ospreys head coach Sean Holley echoes those hopes of his captain, adding: "I just hope we are going to get the same home support that clearly aided Clermont - I thought they were amazing and fantastic.
"Leicester are going really well and they will bring some fans with them. We know how tough it is going to be but, in recent games against the Blues and Munster at the Liberty, the fans have been vocal.
"We've noticed the difference and it has been benefical. The home support in Clermont was amazing and clearly had a psychological effect on the game.
"But then everything about Clermont was to admire. Their pack was mature and heavy, Brock James at No 10 was outstanding and, as well as Dan Biggar played, he was up against a guy who was on top of his game."