Manchester United, Chelsea and Arsenal are among the heavyweight clubs with their hopes still in the balance going into the final matchday of the 2015-16 Champions League group stage.
We look the standings as 13 teams compete for seven places still available in the round of 16 on Tuesday and Wednesday, starting with the competition's most open pool:
Group B - Wolfsburg, Manchester United, PSV, CSKA Moscow
Wolfsburg only need to take a point from their home game against second-placed United to ensure progression and that will also clinch first place in Group B if PSV fail to beat CSKA at home.
United sit just one point behind Wolfsburg and a victory in Germany will see them through to the next round as group winners.
A draw will also be enough, should PSV fail to win, but it would leave United second and at the mercy of a potentially tough round-of-16 opponent.
PSV are guaranteed progression if they beat CSKA, although a draw will also be sufficient in the event of a United defeat in Germany, given their superior head-to-head record.
CSKA can overhaul PSV and book a place in the Europa League by winning in Eindhoven.
Group G - Porto, Chelsea, Dynamo Kiev, Maccabi Tel Aviv (E)
Group G is dramatically poised ahead of matchday six. The top two, Porto and Chelsea are locked on 10 points and meet at Stamford Bridge with the Portuguese side ahead of the Premier League champions courtesy of September's 2-1 win at Estadio do Dragao.
The loser, if there is one, can be overhauled by Dynamo Kiev, who are third on eight points, if they beat eliminated Maccabi Tel Aviv in Ukraine.
If Porto and Chelsea draw and Dynamo win, all three teams will be level on 11 points. They would also have five points apiece from matches against one another, sending the outcome to goal difference from matches between the three. That would see Kiev top the group, with Chelsea second and Porto third.
Group F - Bayern Munich (Q), Olympiacos, Arsenal, Dinamo Zagreb (E)
Third-placed Arsenal travel to Olympiacos, who are three points ahead in second, requiring a 3-2 victory or any win by a two-goal cushion or greater if they are to qualify for the round of 16 and avoid the Europa League.
Bayern Munich are guaranteed top spot in Group F ahead of matchday six, meaning the result of their game against eliminated bottom side Dinamo Zagreb will not have any effect on the rest of the group.
Group E - Barcelona (Q), Roma, Bayer Leverkusen, BATE
With Barcelona running away with Group E, Roma and Bayer Leverkusen, locked on four points will jostle to go through, with BATE also lurking on four points behind them.
A win for Roma at home to BATE will guarantee Rudi Garcia's men second spot, regardless of the outcome of Leverkusen's clash at home to Barcelona, given Roma hold a superior head-to-head record over the Bundesliga club.
If Roma lose, Leverkusen must beat Barca to secure second, while BATE will take third. A BATE win coupled with a Barca victory would see the Belarusian club progress for the first time in their history.
Group H - Zenit (Q), Gent, Valencia, Lyon (E)
Gary Neville's first game in charge of Valencia is a must-win contest at home to Lyon. The Liga club three points of their own as well as Gent failing to beat Zenit - who have won all five of their group games so far - to go through.
Group D - Juventus (Q), Manchester City (Q), Borussia Monchengladbach, Sevilla
Juventus lead Manchester City by two points, with both teams assured of a place in the next round. Juve defeated City home and away and need just a point at Sevilla to guarantee top spot.
If City beat Gladbach and Sevilla overcome Juventus, the Premier League club will top the group and Unai Emery's men will progress to the Europa League - a competition they have won in the past two seasons.
Gladbach will safely progress to UEFA's second-tier competition if Sevilla fail to win.
Group C - Benfica (Q), Atletico Madrid (Q), Galatasaray, Astana
Atletico Madrid and Benfica, level on 10 points in first and second place respectively, will play each other to decide the group winner. A draw at the Estadio da Luz will play into Benfica's hands, having won 2-1 at the Vicente Calderon.
Galatasaray are third, one point above an Astana team who are yet to register a win. The Turkish side drew 2-2 in the reverse fixture in Kazakhstan, are at home in this one and look most likely to take third place and a Europa league spot.
Group A - Real Madrid (Q), PSG (Q), Shakhtar Dontesk, Malmo
The two qualifying spots in Group A are already decided, with Real Madrid first and PSG second.
Malmo are away to Madrid and must better Shakhtar Donetsk's result at PSG to qualify for the Europa League ahead of the Ukrainian club.
