Real Madrid and Atletico Madrid begin their respective Champions League campaigns with huge tests against Paris Saint-Germain and Juventus in the pick of Wednesday's action.
Atletico will be smarting from last season's 3-2 aggregate defeat to Juve in the round of 16, when Cristiano Ronaldo – a consistent nemesis of theirs during his time in LaLiga – netted a hat-trick in a 3-0 second-leg win to see the Old Lady into the quarter-finals.
Madrid get started away to PSG, who will be aiming to continue their fine run at home in the group stage despite being without Neymar, Kylian Mbappe and Edinson Cavani.
Last term's beaten finalists Tottenham, Premier League champions Manchester City and German giants Bayern Munich are also in action.
Below, we have highlighted the key data ahead of Wednesday's contests.
Club Brugge v Galatasaray
4 - After losing their first two matches in the 2018-19 Champions League, Club Brugge remained undefeated in their final four (W1 D3) – should they avoid a loss in this match, it will be the best unbeaten run by a Belgian side in the competition took on its current format in 1992.
12 - Galatasaray's new striker Radamel Falcao has scored 12 goals in the Champions League, just one goal off the record by a Colombian player in the competition: Jackson Martinez with 13.
Paris Saint-Germain v Real Madrid
21- PSG are unbeaten in 21 Champions League home games in the group stage (W15 D6), not losing since December 2004 against CSKA Moscow (1-3).
1.97 - Real Madrid have averaged the most goals per game (2.13) in Champions League history. PSG are third on 1.97, with Barcelona the only club separating them in the rankings (2.02).
Olympiacos v Tottenham
8 - Olympiacos are winless in eight Champions League matches (D1 L7) since a 2-1 win against Dinamo Zagreb in November 2015. It is their joint-longest winless run in the competition alongside a streak that ended in October 2003.
50 - Mauricio Pochettino's will oversee his 50th European game as manager of Spurs on Wednesday. Only Bill Nicholson (55) has presided over more for the club.
Bayern Munich v Red Star Belgrade
36 - Robert Lewandowski has scored 36 goals in just 52 Champions League appearances for Bayern – only Thomas Muller has scored more for the club in the competition (42 goals in 105 games).
17 - Red Star conceded more goals in the group stage of the 2018-19 Champions League than any other team (17).
Dinamo Zagreb v Atalanta
11 - Dinamo Zagreb have lost their last 11 consecutive Champions League matches, their joint-worst run in the competition. Only Anderlecht have lost 12 successive matches in Europe's elite competition, that run coming between December 2003 and November 2005.
3 - Just three of the nine Italian clubs to have participated in the Champions League before Atalanta have won their opening match in the competition: AC Milan in 1992, Juventus in 1995 and Udinese in 2005.
Shakhtar Donetsk v Manchester City
79 - Excluding own goals, 79 of Shakhtar's 124 Champions League goals have been scored by Brazilians (64 per cent) – only Barcelona (85) have seen more goals scored by Brazilians than Shakhtar, while Braga (11-12 – 92%) are the only team to have had a higher proportion of goals scored by players from Brazil.
124 - Gabriel Jesus scored a hat-trick for City in their last meeting against Shakhtar in November last year, inspiring a 6-0 win. Of the 73 Brazilians to have scored four or more goals in the Champions League, Jesus has the best minutes-per-goal (124) ratio.
Atletico Madrid v Juventus
54 - Atletico will be competing in their first Champions League season without Antoine Griezmann since 2013-14. He scored or assisted 54 per cent of their goals in the competitions (19 goals, 7 assists) between September 2015 and March 2019 before leaving this year for Barcelona.
25 - Juventus star Ronaldo has scored 25 goals in his career against Atletico, having tormented them regularly in derbies with Madrid and netted a hat-trick last term for the Bianconeri. Only against Sevilla (27) has he scored more in all competitions.
Bayer Leverkusen v Lokomotiv Moscow
0 - Bayer Leverkusen coach Peter Bosz has yet to win a Champions League game as a manager (D2 L4, with Dortmund). Each of Leverkusen's past four managers have failed to win their first Champions League match in charge.
7 - Lokomotiv forward Jefferson Farfan will be looking to score in his seventh different Champions League campaign (2004-05, 2005-06, 2007-08, 2010-11, 2012-13 and 2018-19). The only Peruvian to have scored in more seasons is Claudio Pizarro (eight).