Paris Saint-Germain will be out for revenge when they face Manchester City in a blockbuster Champions League clash.
City reached their first Champions League final last season by beating PSG 4-1 on aggregate last season and they will meet again in a Group A clash at the Parc des Princes.
PSG were held by Club Brugge in their opening game, while Premier League champions City hammered RB Leipzig 6-3.
Milan face Atletico Madrid in their first home match in Europe's premier cup competition since 2014.
Leaders Liverpool travel to Porto in the other Group B game with fond memories of their previous two trips, while Real Madrid entertain Sheriff in the battle between the top two in Group D.
Here, Stats Perform look at the key Opta data ahead of the games taking place on Tuesday.
Paris Saint-Germain v Manchester City: Messi could face another Guardiola reunion
Lionel Messi, who was linked with City before his sensational move to PSG, has been sidelined be a knee problem and it remains to be seen if he recovers in time for a reunion with his former boss Pep Guardiola.
PSG and City will meet for the sixth time, while the Ligue 1 side still looking for their first win in this fixture (D2 L3). Only against Juventus (8) have they played more games in European competition without winning.
City are unbeaten in 10 away Champions League away games (W8 D2), not losing in the competition outside of England since December 2017 (against Shakhtar Donetsk).
Milan v Atletico Madrid: Rossoneri eyeing happy homecoming
Milan and Atleti's only previous meetings came in the 2013-14 Champions League, with the Rossoneri losing both legs in the round of 16. The clash with the reigning LaLiga champions seven years ago was Milan's last at home in the competition.
Antoine Griezmann is Atleti's all-time top scorer in the European Cup/Champions League (21 goals), and could also become their outright top scorer in away games if he finds the net in this game (currently on five).
In the loss at Anfield, Brahim Diaz (22 years 43 days) became the youngest player to score on his Champions League debut for Milan since Yoann Gourcuff in September 2006 (20 years 64 days v AEK Athens).
Porto v Liverpool: Reds to cut loose again?
This will be the fifth time Liverpool have faced Porto in the Champions League since Jurgen Klopp became the club's manager – they have won more games (3), scored more goals (11) and kept more clean sheets (3) against them than any other opponent in the competition.
Porto have only scored once in those four previous meetings (D1 L3), despite attempting 45 shots. In contrast, Liverpool's 11 goals have come from 54 attempts.
Sadio Mane has been directly involved in five goals against Porto, scoring four times and providing one assist. Mane's four goals are the joint-most by a Liverpool player against an opponent in the competition, along with Steven Gerrard v Marseille and Philippe Coutinho v Spartak Moscow.
Real Madrid v Sheriff: Madrid on brink of century
Madrid are one short of becoming the first team to record 100 home victories in the Champions League. Their win percentage of 73 is the highest for any team in the competition's history with at least 10 home games played (99/136).
Sheriff won 2-0 on their Champions League debut last time out against Shakhtar Donetsk - they are looking to become the first team since Leicester City in 2016-17 to win their first two games in the competition.
Sheriff's Cristiano scored twice on his Champions League debut against Shakhtar, becoming the first Brazilian to score a brace in his first game in the competition since Chelsea’s Oscar in September 2012 (v Juventus).
Ajax v Besiktas
4 - Ajax striker Sebastien Haller scored four goals on his Champions League debut against Sporting CP. If he gets another against Besiktas, he would move clear of a tie with Marco van Basten, Diego Simeone, Didier Drogba and Erling Haaland for the most by a player in their first two appearances in the competition.
2 - Besiktas have conceded at least two goals in each of their previous four games against Ajax (10 in total).
Shakhtar Donetsk v Inter
1 - Shakhtar have only scored one goal in their previous five meetings with Inter and have failed to find the back of the net in the three most recent encounters.
32 - Inter and Shakhtar played out two goalless draws in the Champions League last season despite the Serie A champions attempting 32 shots, with an expected goals total of 3.1 across the two games.
RB Leipzig v Club Brugge
10 - Club Brugge have not won any of their past 10 games against German opponents in European competition (D3 L7).
4 - Christopher Nkunku scored a hat-trick for Leipzig against City, but became just the fourth player in Champions League history to score at least three goals and still end on the losing team.
Borussia Dortmund v Sporting CP
100 - Dortmund have a 100 per cent win record at home to Portuguese opposition in European competition, winning all six of their previous games by an aggregate score of 17-2.
63 - Erling Haaland has averaged a goal every 63 minutes in home games for Dortmund in the Champions League. His seven goals at Signal Iduna Park is the most of any player at a single stadium in the competition since he joined the club.