 The matchdays are 15 September, 29 September, 20 October, 3 November, 24 November, and 8 December 2016.A total of 21 national associations are represented in the group stage.Astana, Celta Vigo, Dundalk, Hapoel Be'er Sheva, Konyaspor, Mainz 05, Manchester United, Nice, Olympiacos, Osmanlıspor, Sassuolo, Southampton and Zorya Luhansk made their debut appearances in the UEFA Europa League group stage (although Celta Vigo and Olympiacos had appeared in the UEFA Cup group stage and Manchester United and Olympiacos had already competed in the UEFA Europa League knockout phase after a third place in the UEFA Champions League group stage).