Barcelona and AC Milan can effectively seal their expected places in the Champions League knockout stage with three games remaining when they play rank outsiders Viktoria Plzen and BATE Borisov respectively in their Group H matches on Wednesday.
European champions Barca, who crushed Borisov 5-0 in Belarus in their last Champions League outing on Sept. 28 are the overwhelming favourites to see off their Czech visitors, who were beaten 2-0 away to Milan last time out.
Barca and Milan, who host Borisov, have four points each from two matches while the other pair both have one and the competition's two giants, who have been European champions 11 times between them, can open a six-point gap with victories.
Both sides have made poor starts to their domestic league campaigns and, while their Champions League performances have been less erratic, they will nervously hope for a victory.
Marseille are top with six points from two games followed by Arsenal on four but with Borussia Dortmund, who travel to Olympiakos, also in the group and looking for a first win, neither side can afford to slip up.
Group E is even tighter with Chelsea on four points, Bayer Leverkusen with three, Valencia on two and Racing Genk with one but things should become clearer, at least for Chelsea who are odds-on to beat the Belgians.
Surprise Group G leaders APOEL Nicosia will be severely tested when they travel to former Champions league winners Porto, who have won 15 of their last 19 European home games.
Shakhtar Donetsk of Ukraine host Zenit St Petersburg of Russia in the other match in the section.