Connacht, Montpellier, Pau, Ospreys and Edinburgh have already qualified for the last 16 and will be joined by 11 more clubs by Sunday evening in the knockout stages.
There are nine games in the final round of Challenge Cup pool matches with 12 teams qualifying for the last 16 from the second tier group stages and four sides dropping down from the Champions Cup.
The four highest-ranked clubs in each of the three Challenge Cup groups will progress alongside the fifth-ranked clubs from the four Champions Cup sections.
In terms of knockout stages rankings, the clubs will be put in descending order based on their placings in their pool and then on the number of match points they have accumulated to create an overall list from 1 to 16.
The Challenge Cup pool winners will be ranked one to three with the top two teams having potential home advantage until the final.
The second-placed sides will be between four to six and the two highest-ranked third-placed clubs will be placed at seven and eight. Those eight sides will have home advantage.
The four teams that drop down from the Champions Cup will be ranked nine to 12 and the remaining quartet of Challenge Cup sides who have qualified will make up the final four spots from 13 to 16.