The two sides, champions in their domestic leagues last season, have experienced drastically contrasting fortunes this time around, with many tipping the German giants to be far too strong for their faltering opponents over two legs.
Bayern come into Tuesday's first leg at Old Trafford on the back of a 3-3 draw against Hoffenheim in the Bundesliga on Saturday, only the third time this season that Pep Guardiola's men have dropped points in the league.
Having already clinched the Bundesliga with a 2-1 win at Hertha Berlin last Tuesday, Guardiola rested several key players on Saturday as Bayern shift their focus to defending their continental crown.
A host of first-team regulars started on the bench, including the likes of Thomas Muller, Phillip Lahm and Arjen Robben, although Lahm was introduced after 25 minutes when Thiago Alcantara had to be withdrawn after suffering a knee ligament tear which will keep the Spaniard out for six to eight weeks.
On the other hand, United have followed romping to the Premier League title by 11 points last term with a season of struggle under new manager David Moyes as they enter a new era following Alex Ferguson's retirement.
Ferguson famously oversaw United's incredible comeback in the 1999 Champions League final, when stoppage-time strikes from Teddy Sheringham and Ole Gunnar Solskjaer broke Bayern hearts, and the competition has been a rare source of comfort for Moyes in an otherwise disappointing campaign.
Sitting 10 points adrift of the Premier League's top four with only six games remaining, United's best chance of securing a place at Europe's top table next season looks to be by winning the title, although they will start this tie as underdogs.
They produced a stirring comeback in the round of 16, losing 2-0 to Olympiacos in Greece before Robin van Persie's hat-trick turned the tie around at Old Trafford.
However, the Dutchman will miss out against Bayern due to a knee injury suffered in that win, with Moyes also facing a shortage at right back in Chris Smalling (hamstring), Rafael da Silva (knock) and Antonio Valencia's (knee) collective absence.
Both sides will be forced to manage without first-choice selections in the backline, with United's Patrice Evra and Bayern's Dante serving one-match suspensions.
Moyes' men have won all of their home games in this year's competition, but that record will be severely tested against a Munich side that has not lost away from home in the Champions League since October 2012.
Bayern overcame English opposition in the last round, beating Arsenal 3-1 on aggregate and also knocked United out on their way to the 2010 final at the same stage they meet this year.
