What is each club's pedigree? Who are their key players, new faces and ones to watch? UEFA.com has all the answers.
Article top media content
UEFA coefficient ranking (end of 2018/19): 5
How they qualified: Italian champions
European Cup best: winners x2 (most recently 1996)
Last season: quarter-finals (lost 3-2 on aggregate to Ajax)
Group stage last season: Group H winners – W4 D0 L2 F9 A4 (v Manchester United, Valencia, Young Boys)
In: Aaron Ramsey (Arsenal), Adrien Rabiot (Paris), Matthijs de Ligt (Ajax), Danilo (Manchester City), Gianluigi Buffon (Paris)
Out: Leonardo Spinazzola (Roma), Moise Kean (Everton), João Cancelo (Manchester City), Andrea Barzagli (retired)
Coach: Maurizio Sarri
Only an amateur as a player, Sarri is approaching 30 years as a coach. Led Empoli into Serie A in 2014 before making his name at Napoli with a fast-paced, possession-based style of attacking football that became known as 'Sarriball'. Spent last season at Chelsea, winning the UEFA Europa League and reaching the English League Cup final before returning to Italy in the summer.
Key player: Cristiano Ronaldo
The UEFA Champions League's all-time leading scorer (126 goals) scored five of his six in last season's competition in the knockout stage, including a memorable hat-trick that turned their round of 16 tie against Atlético Madrid on its head. Passed 400 career league goals last term and helped Portugal to UEFA Nations League glory.
One to watch: Merih Demiral
The transfer of Matthijs De Ligt may have grabbed the headlines, but a deal for another centre-back may prove equally important in the long term. The tall defender, 21, made his senior Turkey debut in November and has been widely compared with former national-team regular Alpay Özalan. May get his chance at Juventus this season due to Giorgio Chiellini's knee injury.
UEFA coefficient ranking (end of 2018/19): 4
How they qualified: second in Spanish Liga
European Cup best: runners-up x3 (most recently 2016)
Last season: round of 16 (lost 3-2 on aggregate to Juventus)
Group stage last season: Group A runners-up – W4 D1 L1 F9 A6 (v Dortmund, Club Brugge, Monaco)
In: Marcos Llorente (Real Madrid), Héctor Herrera (Porto), João Félix (Benfica), Kieran Trippier (Tottenham)
Out: Lucas Hernández (Bayern), Diego Godín (Inter), Antoine Griezmann (Barcelona), Rodri (Man. City), Filipe Luís (released)
Coach: Diego Simeone
A combative holding midfielder with the likes of Atlético, Internazionale and his native Argentina, Simeone took the reins of the Madrid club in December 2011. Now 49, he has since led Atlético to the UEFA Champions League final twice, the UEFA Europa League title twice, the UEFA Super Cup twice, the Spanish Liga and the Copa del Rey.
Key player: Jan Oblak
Simeone's side have been as resolute defensively as any side in Europe over recent seasons, but the departures of Lucas Hernández, Diego Godín, Juanfran and Filipe Luís over the summer will test their rearguard to the limit. In Oblak, though, they still have one of the best goalkeepers on the continent and someone capable of marshalling their new recruits.
One to watch: João Félix
The fourth most expensive signing in the game's history has huge shoes to fill following Antoine Griezmann's move to Barcelona. His performances in his first season with Benfica last term suggest he is capable of rising to the challenge – a haul of 20 goals in 43 games in all competitions at the age of 19. Three of those came in the UEFA Europa League quarter-final first leg against Frankfurt, making him the youngest player ever to score a hat-trick in the competition.
UEFA coefficient ranking (end of 2018/19): 28
How they qualified: fourth in German Bundesliga
European Cup best: runners-up (2002)
Last season: #UEL round of 32 (lost on away goals, 1-1 on aggregate, to Krasnodar)
In: Kerem Demirbay (Hoffenheim), Moussa Diaby (Paris), Nadiem Amiri (Hoffenheim)
Out: Thorsten Kirschbaum (VVV), Julian Brandt (Dortmund), Dominik Kohr (Frankfurt)
Coach: Peter Bosz
Won the Eredivisie as a midfielder with Feyenoord in 1993 and picked up eight caps for the Netherlands during his playing days. Coached several clubs in his home country, enjoying the most success with Vitesse and then Ajax, whom he led to the 2017 UEFA Europa League final. Spent just six months at Dortmund the following season but has fared better at Leverkusen, winning more than half of his games since taking over.
Key player: Kai Havertz
The midfielder is still only 20 but has broken into the Germany side off the back of a sensational season at Leverkusen, where he struck 17 Bundesliga goals and another three in the UEFA Europa League. Technically gifted, two-footed and composed on the ball, the youngest player to reach the milestone of 50 Bundesliga appearances has been tipped for even greater things this season.
One to watch: Moussa Diaby
Unable to secure a regular place in an all-star Paris attack, despite 34 appearances in all competitions last season, Diaby moved to Germany this summer. Leverkusen have plenty of previous form when it comes to recruiting skilful wingers, so expect the 20-year-old to seize the opportunity.
UEFA coefficient ranking (end of 2018/19): 54
How they qualified: second in Russian Premier League
European Cup best: last 16 x2 (most recently 2004)
Last season: group stage (fourth place)
Group stage last season: fourth place in Group D – W1 D0 L5 F4 A12 (v Porto, Schalke, Galatasaray)
In: Murilo Cerqueira (Cruzeiro), Grzegorz Krychowiak (Paris), João Mário (Inter, loan)
Out: Vitaliy Denisov (released), Dmitri Tarasov (released), Igor Denisov (retired), Taras Mikhalik (Volyn)
Coach: Yuri Semin
Semin was a midfielder or striker in his playing days, representing the likes of Spartak Moskva, rivals Dinamo and Lokomotiv. He started coaching at Pamir in 1983 but made his name at Lokomotiv, where he impressed from 1986 to 2005. Two spells at Dynamo Kyiv are among his subsequent roles and he has been back at Lokomotiv since 2016.
Key player: Grzegorz Krychowiak
The Polish midfielder's experience proved crucial in Lokomotiv securing UEFA Champions League football again following their Russian title in 2017/18 and he joined the club on a permanent basis this summer.
One to watch: Dmitri Barinov
The 22-year-old central midfielder made 33 appearances in all competitions last season and won his first two caps for Russia this summer.
Did you know?
- Juventus beat Atlético in last season's round of 16 thanks to a second-leg hat-trick from Cristiano Ronaldo (0-2 a, 3-0 h).
- Cristiano Ronaldo has scored seven goals in his past eight UEFA competition meetings with Atlético but has never faced Leverkusen or Lokomotiv in Europe.
- Atlético beat Lokomotiv 3-0 at home and 5-1 away in the round of 16 of their victorious UEFA Europa League campaign in 2017/18.
- Juventus were 4-0 aggregate winners against Lokomotiv in the 1993/94 UEFA Cup first round; Atlético have scored 11 goals in their three matches against the Russian club (W2 D1).