Arsenal winger Max Dowman could become the youngest player in Champions League history if he features for Athletic Bilbao when the revamped group stage kicks off on Tuesday. Dowman, who became the second youngest Premier League player last month, is 15 years and 259 days old.
This is the second season under the league phase format, with 36 teams facing eight different opponents on a weighted schedule through January, all ranked in a single table. The first round of matches is spread over three days this week.
Record 15-time champions Real Madrid host Marseille, needing just one win and two goals to reach milestones of 200 wins and 700 goals in the competition. Madrid has defeated Marseille in all four previous European encounters.
Belgian champions Union Saint-Gilloise make their Champions League debut at PSV Eindhoven, while Qarabag travels to Benfica. Tottenham faces Villarreal, and new Juventus signing Jonathan David, who has scored seven goals in his last nine league matches, will feature as the Bianconeri host Borussia Dortmund.
The top eight teams in the standings will advance directly to the round of 16, while the next 16 teams enter a two-leg playoff, with eight advancing to the knockout stage.