Both may have already secured a Top 14 play-off berth but home advantage will be at stake when Racing-Metro host Castres at the Stade Colombes on Saturday.
Parisians Racing currently sit fifth in the Top 14 table, one place below Castres, knowing they must leapfrog their weekend visitors in order to gain the benefit of playing at home when the play-offs begin a week later.
Racing trail Castres by four points so really need to win with an attacking bonus point -- awarded to a team if they score at least three more tries than their opponents -- if they are to claim fourth place.
If they were to fail to do so, they would need a minimum 21-point victory in order to overtake Castres, who themselves have an eye on overtaking Toulouse for third place, although with the reigning champions hosting little Grenoble, that would seem a far-fetched proposition.
It means this is the one fixture that will be fiercely contested at a time of the season when games can often become meaningless processions with the major issues already decided.
And Castres's backs coach Laurent Labit has left no doubt as to how important he feels home advantage could be in the play-offs.
"There are two sets of coaching staffs and each one is defending their colours, and neither one wants to give the other a present," said Labit, who along with Castres's forwards coach Laurent Travers, will be coaching Racing next season.
Beforehand, they want to go out with a bang and take Castres further than they have done in the past, having secured a play-off spot for the third year in a row.
Last year they made it to the semi-finals where Toulouse put an end to their run with a 24-15 success.
If they are to set their sights on a final this time around, avoiding a tricky away trip in the first round of play-offs would give them a helping hand.
If Castres were to lose, they might not only be overtaken by Racing, but also by Montpellier, who host Perpignan.
Montpellier, who can count on fit-again France fly-half Francois Trinh-Duc once more, need to win with a bonus point and hope Racing beat Castres with neither side taking a bonus in order to snatch fourth spot.
With such permutations, Castres know they simply need to win to ensure they'll be at home next week.
Even though Labit and Travers are heading to Racing during the summer break, the backs coach insists there will be no hint of divided loyalties at Colombes.
They already proved that by turning over their Parisian visitors 31-10 earlier in the season, soon after the announcement of their new destination.
"If we had to do it again, we'd deal with it in the same way," Labit said about the timing of their announcement.
"Just as much for the club we're quitting to organise the succession as to prepare our arrival at Racing," added Labit.
In the meantime, the only other issues to be decided are exactly who finishes top, with Clermont leading Toulon by a point, although they play at home to Bordeaux-Begles and relegated-Agen respectively.
Agen have hardly helped their preparation for the trip to Toulon -- who have promised to play a strong line-up to maintain their intensity ahead of a May 18 European Cup final with Clermont -- as their players refused to train Thursday during to concerns over the club's financial problems.
Biarritz v Stade Francais
Clermont v Bordeaux-Begles
Mont-de-Marsan v Bayonne
Montpellier v Perpignan
Racing-Metro v Castres
Toulon v Agen
Toulouse v Grenoble