Arsenal and Manchester United will look to improve on their last Champions League performances when they entertain Hamburg and Celtic on Tuesday night, in a bid to reach the knockout stages.
Arsenal have lost their way recently, although a home match against Hamburg SV on Tuesday should calm their jitters in a tight Group G.
The London club have seven points, level with Porto, and one behind group leaders CSKA Moscow, but visit the Portuguese side in their final match so victory over Hamburg is crucial.
Arsenal are likely to be without Dutchman Robin van Persie who injured his foot in the disappointing 1-1 home draw with Newcastle United on Saturday.
CSKA would reach the last 16 if they beat Porto.
In Group F, Celtic striker Kenny Miller has tried to bolster confidence ahead of the Champions League clash with Manchester United by insisting Sir Alex Ferguson's side are 'not immortal'.
United maintained a three-point lead over Chelsea at the top of the Premiership with a 2-1 win at Sheffield United on Saturday.
They also sit top of Group F with nine points, three of which were gained in a 3-2 victory over Celtic at Old Trafford in September.
The Red Devils are odds-on to beat the Hoops for a second time and ensure qualification for the knockout stages.
However, Miller has not forgotten United's defeat in Copenhagen earlier this month as well as their Carling Cup exit at lowly Southend and said: `'We need to get something from the game, there's no doubt about it.
'But it has been shown that they can be beaten, they are not immortal. They are a good team, don't get me wrong, but we can beat them.'
In Group E, Real Madrid, unlike their arch-rivals Barcelona, are already in the last 16, although they face a formidable task against group leaders Olympique Lyon on Tuesday.
The French champions have a 100 percent record and a point in the Bernabeu will clinch first place in the group.
'We will have to be careful. We know that they have improved a lot since we last met,' Lyon's France defender Sebastien Squillaci said of Real, who they beat 2-0 at home.
Real are third in the Primera Liga after a 3-1 victory over Racing Santander on Saturday.
Lille will hope to become the second French club into the last 16 by beating Anderlecht in Group H on Tuesday.
The northern side will achieve that feat if they win and AEK Athens fail to beat group leaders AC Milan.
'Tuesday's game is one of the most important in the club's history,' said Lille defender Mathieu Chalme.
Like Real Madrid and Lyon, a place in the last 16 is also assured for Bayern Munich, Liverpool, PSV Eindhoven and Valencia while Manchester United need one point at Celtic.
Holders Barcelona would have expected to be safely installed in the last 16 of the Champions League by now instead of facing an anxious night in Bulgaria knowing anything less than victory could knock them out.
Frank Rijkaard's side find themselves in third place in Group A with five points, having won just one of their four matches so far, and even if they do beat hapless Levski Sofia on Wednesday their fate will not be decided until the final group game when they host Werder Bremen.
The German club, who have seven points, host leaders Chelsea (10 points) on Wednesday buoyed by the knowledge that the English champions are far less formidable on the road in Europe where they have won just two of their last 10 away games.
Should Bremen win and Barca drop points it would mean the Catalans having to content themselves with a humbling place in the second-tier UEFA Cup.
Bremen, though, are out of form after needing a late Miroslav Klose goal to salvage a 2-2 draw with lowly Alemannia Aachen at the weekend, and they cannot expect any favours from Chelsea, despite what the conspiracy theorists might say.
Chelsea boss Jose Mourinho, public enemy number one at the Nou Camp, said his side will go all out for victory, despite a huge Premier League clash with Manchester United next weekend.
'The game against Werder Bremen is a game that can influence the future of the Champions League so we have responsibilities,' Mourinho said after Chelsea's 1-0 win over West Ham United on Saturday.
'We need to play a serious game. We cannot go there like some people were expecting, with a second team -- Bremen beat Chelsea, maybe Barcelona is out of the competition.
'That's not our war, that's not our problem. We go there to try to get a result.'
Germany playmaker Michael Ballack, rested against West Ham, is likely to return as Mourinho backs up his promise.
While Barca and Bremen battle for position, however, others such as Italian champions Inter Milan and Roma still have work to do.
Inter are second in Group B with six points and can join Bayern in the next round if they beat third-placed Sporting Lisbon (five points) in the San Siro on Wednesday.
Likewise, Roma can secure their path out of Group D along with Valencia if they take a point from a tricky trip to Shakhtar Donetsk and will certainly be confident after a 7-0 thrashing of Catania on Sunday.