For reigning champions Milan, Barcelona and Real Madrid one point will suffice but for others, notably five-times European champions Liverpool, the journey has become a white-knuckle ride with no more margin for error.
Two defeats and a draw from their first three matches in Group A left Liverpool in the mire and needing a Houdini-like escape act to stay alive.
Three victories were required and while Besiktas were duly thumped a record 8-0 at Anfield in the last round of fixtures, group leaders Porto will prove a far sterner test on what will be a highly-charged night at Anfield on Wednesday.
The slick Portuguese can secure their place in the knockout round with a victory, although a draw would be sufficient as long as Besiktas do not beat second-placed Marseille.
Portuguese clubs have troubled Liverpool before, most notably two years ago when Benfica knocked them out in the last 16, but manager Rafael Benitez believes the gravity of the situation could work in his side's favour.
"I am confident we can do it," Benitez, whose job is rumoured to be under threat, told the club's Web site. "We are a team that can play under strain and stress. We have proved that.
"We have had our problems in the group and we found it hard in the game against Porto over there. But there is a big difference. What we have to do is clear -- and I believe we can do it.
"Porto cannot afford to just sit back. If Besiktas beat Marseille they will have a big opportunity to go through in the last game so Porto have to come here and try to win -- and that should help us." Steven Gerrard's form in the 3-0 win at Newcastle United on Saturday bodes well for Liverpool but they will need another barnstorming display from their skipper.
Valencia's prospects are even bleaker than Liverpool's as their fate is not even in their own hands after a desperately disappointing campaign in Group B.
They sit bottom with three points and must beat Schalke, one of three struggling German clubs, at home on Wednesday to have any chance of making progress.
Group leaders Chelsea will be wary of a trip to surprise package Rosenborg after the Norwegians drew at Stamford Bridge and beat Valencia home and away to sit second. Victory would send Chelsea through but Rosenborg will be fired-up with a last 16 place within touching distance.
All four Italian heavyweights are in good shape. Milan travel to Benfica in Group D knowing a draw will be good enough, Inter host Fenerbahce in Group G in a match that will result in qualification for whoever wins.
Lazio are at home to Olympiakos with three points probably enough and Roma will surely beat a dispirited Dinamo Kiev in a freezing Ukraine even without Francesco Totti.
The stakes will be high at Celtic Park on Wednesday where Celtic play Shakhtar Donetsk. Both have six points and whoever wins will be favourites to join Milan in the next round.
Sevilla will be hoping Arsenal rest some of their big names when they host the already-qualified English leaders on Tuesday. After defeat in their Champions League debut by the Gunners, Sevilla have recovered well and victory could even allow them to snatch top spot in Group H.
