It could be said that every night in the Champions League is an improtant one, but for Chelsea and Celtic, tonight is definitely make or break for both Chelsea and Celtic.
A defeat for defending champions Chelsea against Italian champions Juventus tonight would mean that there is a more than significant chance of them becoming the first champions not to progress to the knockout stages.
Although they sit top of their group, level on 7 points with the Italian champions, Shakhtar Donnesk sit only a point behind. A defeat, coupled with Donnesk's widely expected win over group minnows FC Nordsjaelland tonight would leave Chelsea three points behind Juventus and two behind Donnesk, meaning they would have to win their final match to ensure qualification.
A win in itself would not be enough to guarantee a spot, as they could still go out if they lose their final match and Juventus win theirs. This piles more pressure on Roberto Di Matteo, who saw his side drop yet more points in the Premier League after a defeat by West Brom at the weekend.
Celtic can qualify with a win tonight if they overcome Benfica tonight, and will be buoyed by their recent form, most notably the historic win over Barcelona in the last round of games.
But a loss could put their hopes in jeopardy, as both teams below them can still qualify with wins in their remaining matches.
Manchester United face a much less stressful evening, having already ensured they will qualify top of their group, and boasting the only 100% record in the competition.
With big names such as Rooney, Evra and Van Persie left at home, it will be a good opportunity for Sir Alex Ferguson to cast his eye over his current crop of young starlets, with players such as Nick Powell, signed in the summer, looking to start the game.