Tuesday night's must-win clash in Wolfsburg is the club's biggest since the retirement of Sir Alex in 2013.
We travel to the Volkswagen Arena having not won on the road in the Champions League proper so far this term while our opponents boast a formidable record on their own turf- seeing a 29-match unbeaten league run ended by Dortmund on Saturday having won both of the European ties on home soil.
Louis van Gaal has done a lot of good things as United boss but there are some fans who doubt whether there's enough attacking intent in his 'philosophy' to win a match when it matters most.
United are organised, efficient and hard to beat but a draw in Germany might not be enough and if we go out on the back of (another) goalless draw, the fans will be on the brink of revolt.
Winning in Wolfsburg is a very difficult proposition under any circumstances, but going there as we are with a catalogue of injury problems will mean that we need our big game players to stand up and be counted.
Anthony Martial looks out most likely match-winner... he may be struggling for form but has the pace and skill to ask questions of their defence and a counter-attacking game plan will suit his capabilities.
In a match we have to win I would give Memphis Depay a go from the start: he was one of our best players against West Ham despite only being on the field for around 15 minutes.
He's one of LVG's few match-winners and, although his talent and temperament can fluctuate, he was terrific on Saturday with and without the ball and he, along with Martial, can be the key to victory.
Tuesday's match will a massive test in every sense: how our young players will handle the atmosphere, intensity and magnitude of the occasion and a chance for LVG to silence the doubters and give the whole club a lift.
The implications of an early exit don't bear thinking about: not only financially (potentially affecting transfer market dealings) but the prospect of Europa League football in February is not one any of us want to think about.