In each group, teams played against each other home-and-away in a round-robin format. The group winners and runners-up advanced to the round of 32, where they were joined by the eight third-placed teams of the 2017–18 UEFA Champions League group stage. The matchdays were 14 September, 28 September, 19 October, 2 November, 23 November, and 7 December 2017.