London Irish and Gloucester's back-to-back ties begin in Reading and promise to decide the destiny of Pool 1 and which one of the English sides will qualify for the quarter-finals.
Irish have rattled off two bonus point wins and lead the Pool by a point and they recorded a comfortable 11-try victory over French side Mont-de-Marsan at the Madjeski Stadium in their last outing.
Wing Topsy Ojo and full back Anthony Watson both scored a brace of tries against the French side to complete their second clean sweep of points in this season's tournament.
Gloucester came through an altogether tougher examination with a 25-13 victory over Bordeaux-Begles at Kingsholm to keep them in touch with their English Premiership rivals.
Mont-de-Marsan and Bordeaux Begles, the two French teams in the Pool, have managed a point between them and their hopes of qualification for the quarter-finals are slim.
But they will be looking to secure the bragging rights over each other in an all French derby, which kicks off with Bordeaux Begles hosting the first of their two games against Mont-de-Marsan.
