A first-ever meeting of Barcelona and Ajax, two of European football's most famous names, tops the billing in Wednesday's Champions League card, while Jose Mourinho's Chelsea and last season's runners-up Borussia Dortmund are also in action.
CHELSEA V BASEL
Jose Mourinho's quest to win the Champions League with Chelsea recommences with a home fixture against the Swiss champions Basel at Stamford Bridge. These clubs met as recently as May, with Chelsea winning 5-2 on aggregate in the semi-finals of the Europa League on their way to lifting the trophy with a final victory against Benfica in Amsterdam. However, they only dropped into that competition after being eliminated from the Champions League at the group stage. This season's draw is a kind one, however, and the London club will be confident of getting back on track after Saturday's Premier League loss at Everton, even if they must do without the suspended Ramires.
SCHALKE 04 V STEAUA BUCHAREST
After a troubled start to the campaign, Schalke's confidence has been lifted thanks to a run of three consecutive victories. The most recent of those was a 1-0 triumph away to Mainz in the Bundesliga on Saturday, secured thanks to Kevin-Prince Boateng's first goal for the club. Boateng returned to Germany after scoring twice for AC Milan in their play-off round win over PSV Eindhoven, although he is eligible to represent Schalke in the group stage and will have an important role to play for Jens Keller's side, who have been without Klaas-Jan Huntelaar recently due to a knee injury. Romanian champions Steaua, the 1986 European Cup winners, came through three qualifying rounds to return to the group stage for the first time since 2008-09.
MARSEILLE V ARSENAL
Arsenal have injury problems, with Santi Cazorla joining the likes of Alex Oxlade-Chamberlain and Lukas Podolski on the sidelines, but the signing of Germany star Mesut Ozil has lifted the London club and he helped inspire them to a 3-1 win at Sunderland in the Premier League on Saturday. That was a fifth consecutive win for Arsene Wenger's side in all competitions ahead of their visit to familiar foes Marseille. The clubs met in the group stage of the same competition two years ago, with Arsenal winning 1-0 in the south of France before a goalless draw in London. Elie Baup's side, who needed a late goal to draw 1-1 at Toulouse in Ligue 1 on Saturday, are the outsiders in a testing group.
NAPOLI V BORUSSIA DORTMUND
Last season's Champions League runners-up kick-off their campaign with a trip to Naples, in what is a contender for the outstanding game of matchday one. Jurgen Klopp's side are top of the Bundesliga having won all five matches so far, including a 6-2 trouncing of Hamburg on Saturday. Summer signings Pierre-Emerick Aubameyang and Henrikh Mkhitaryan were both on target in that game, and Dortmund could scarcely be in better shape ahead of this match at the Stadio San Paolo. Napoli, however, also boast a perfect record in Serie A, with summer recruits Gonzalo Higuain and Jose Callejon netting in Saturday's 2-0 home win against Atalanta. They return to the Champions League after a year's absence having lost to Chelsea in the last 16 two years ago. This time they are coached by a European specialist in Rafael Benitez, the mastermind of Liverpool's 2005 triumph and Chelsea's Europa League victory last season.
ATLETICO MADRID V ZENIT ST PETERSBURG
Europa League winners twice in the last four seasons, Diego Simeone's side return to Europe's leading club competition fresh from winning their opening four games in La Liga. The most recent of those was a 4-2 defeat of Almeria on Saturday, featuring goals by strike duo Diego Costa and David Villa. Brazilian frontman Costa will not be able to play in Wednesday's game at the Vicente Calderon due to a suspension carried over from last season, though, and Atletico can expect a stern test from big-spending Zenit. The Russians will be eager to do better than last season, when they failed to make it beyond the group stage, and warmed up with a 2-0 win against Rostov on Saturday, which left them in second place in the Russian Premier League.
AUSTRIA VIENNA V PORTO
Portuguese champions Porto begin their Group G campaign at the scene of one of their greatest triumphs, with their match against Austria Vienna being played at the Ernst-Happel Stadion. It was there that Porto won their first European Cup in 1987, Rabah Madjer's legendary backheeled effort helping them come from behind to beat Bayern Munich 2-1 in the final. Porto lost the likes of James Rodriguez and Joao Moutinho over the summer, and have a new coach this season in Paulo Fonseca, but they have proven adept at rebuilding quickly in the past and still boast greater experience than their hosts, who are competing in the group stage for the first time. Nenad Bjelica's side came through two qualifying rounds to get here, but warmed up for this game by losing 3-2 at home to Groedig in the Austrian Bundesliga on Saturday.
BARCELONA V AJAX
Group H brings together four former winners of the trophy, and both Barcelona and Ajax have been European champions on four separate occasions. The links between Barca and Ajax are plentiful, notably thanks to Johan Cruyff, who starred as a player and a coach for both sides. Rinus Michels and Louis van Gaal also coached both sides, while former Ajax player Frank Rijkaard led the Catalans to Champions League glory in 2006. Remarkably, though, this will be the first-ever competitive meeting of the two clubs. While the Dutch champions will arrive at the Camp Nou led by Frank de Boer, who spent four years as a player at Barcelona, the match will be an entirely new experience for his opposite number in the dugout. Tata Martino, who has overseen four wins out of four so far in La Liga, has plenty experience of South America's Copa Libertadores, but none of the Champions League.
AC MILAN V CELTIC
Seven-times European champions Milan entertain 1967 winners Celtic in Italy in a repeat of a 2007 last-16 tie, which the Serie A club won 1-0 after extra-time thanks to a Kaka goal. The Brazilian has recently returned to the San Siro after four years with Real Madrid but will miss Wednesday's game due to injury. Milan needed two late goals to earn a 2-2 draw at Torino on Saturday and also had to come through a play-off against PSV Eindhoven to reach the group stage. Massimiliano Allegri's side will be very much the favourites to get the better of the Scottish champions, who needed to win three qualifying ties to get this far. All-conquering at home, Neil Lennon's Celtic were comfortably beaten by another Italian club, Juventus, in the last 16 of this competition last season.