Barcelona begin their champions league title defence on Tuesday night with a highly anticipated clash with Italian champions AC Milan in Group H.
Boss Pep Guardiola will have influential captain Carles Puyol back in the fold after recovering from a knee injury while on the other side of the field Milan will be without Zlatan Ibrahimovic after the former Barca striker suffered a groin strain in training.
Elsewhere in the group Czech republic champions Viktoria Plzen host Belarussian domestic league title holders Bate Borisov.
Chelsea begin their quest to win the trophy they so highly desire with a home game against Bayer Leverkusen in group E.
Coach Andre Villas-Boas makes his European bow with the Blues but will be without injured veterans Didier Drogba and Michael Essien as well as ineligible duo Romelu Lukaku and Ryan Bertrand.
Leverkusen midfielder Michael Ballack returns to Stamford Bridge where he spent four years.
The Germany captain said: ‘‘I always feel welcome with the fans, with the club, they treat me always very well. With the success we had it could have been a few titles more, like you said we missed a few chances. But we still had success and I remember this always and it is always part of my career’‘.
Also on Tuesday night in group E Belgian champions Racing Genk entertain the Spaniards of Valencia on their return to the champions league group stage for the first time in nine years.
Bundesliga champions and former winners Borussia Dortmund host Arsenal in their group F opener.
Both sides have suffered a poor start to their respective domestic leagues with Arsenal picking up their first win in four matches last weekend against Swansea while the Germans have only won twice in their opening five games.
Gunners boss Arsene Wenger meanwhile starts the first of his two-match touchline ban for breaking the conditions of a previous UEFA punishment.
Also on Tuesday Olympiakos host struggling Marseille.
Europa League champions Porto welcome Ukrainian champions Shakhtar Donetsk at the Estádio do Dragão in their group G opener.
Last season’s Portuguese league winners are full of confidence heading into the match after winning their four opening games in the domestic league but defender Rolando and midfielder Guarin will miss the tie on Tuesday through suspension.
Completing group G are Cypriot First Division champions APOEL Nicosia and russian champions Zenit St. Petersburg with the pair squaring up in Nicosia.