The knock-out stage of the tournament was rescheduled from April and May to September and October 2020 due to the COVID-19 pandemic, with the final, originally scheduled for 23 May 2020 at the Stade Vélodrome in Marseille in France, taking place on 17 October 2020 at Ashton Gate in Bristol.

[2] Twenty clubs from the three major European domestic and regional leagues competed in the Champions Cup.

Note: Placing shown in brackets, denotes standing at the end of the regular season for their respective leagues, with their end of season positioning shown through CH for Champions, RU for Runner-up, SF for losing Semi-finalist, QF for losing Quarter-finalist, and PO for the Pro14 7th place play-off winner.

For the purpose of creating the tiers, clubs are ranked based on their domestic league performances and on their qualification for the knockout phases of their championships, so a losing quarter-finalist in the Top 14 would be seeded below a losing semi-finalist, even if they finished above them in the regular season.

[6] Teams in the same pool play each other twice, at home and away, in the group stage that begins on the weekend of 15–17 November 2019, and continues through to 17–19 January 2020.