Of the four teams, Leinster, Clermont and Toulon have already qualified for next season's Heineken Cup by finishing in the upper echelons of their domestic leagues.
Stade Francais, however, must win the Amlin CC if they are to return to the Heineken Cup.
That is their only route into the top tournament, while beaten Amlin CC semi-finalists Perpignan know that their place is secure if Stade Francais lose.
They are the seventh ranked team in the Top 14 and will gain the extra place secured through a French winner of the Heineken Cup provided Stade don't claim it with an Amlin CC triumph.
A Leinster victory, therefore, will not only make Perpignan's day, but also secure a fourth ticket into the Heineken Cup for fellow countrymen Connacht for the third season in a row.
The winners of both the Amlin CC and Heineken Cup get an automatic entry into the Heineken Cup for themselves, or for a team in their country, unless their country already has their maximum permitted quota.
If there are two French winners, then Stade Francais will duly take the seventh place and ERC will go to their rankings for the highest placed team that hasn't already qualified for the Heineken Cup.
In this case a French double will mean Heineken Cup rugby for London Wasps.