The Premier League has provided three of the four semi-finalists for each of the last three seasons but this year has already seen a much-needed levelling out, with six countries represented in the last eight for the first time since 1998/99.
United, missing injured England striker Wayne Rooney for Wednesday's game, have the record books against them as they attempt to overturn a 2-1 first-leg deficit against a Bayern Munich team which has grown in confidence during the season.
Injury-hit Arsenal must either win or pull off a high-scoring draw away to holders Barcelona on Tuesday after last week's thrilling 2-2 draw when they came from 2-0 down after being outplayed for much of the game.
In the other matches, Girondins Bordeaux, trailing 3-1 from the first leg, need to become the first team since 2004 to overturn a two-goal leg deficit in the competition's knockout stages when they host Olympique Lyon in an all-French tie.
Serie A champions Inter Milan defend a 1-0 lead on CSKA Moscow's artificial pitch, which coach Jose Mourinho nonchalantly described the surface as "child's play."
The contests are likely to make nervous viewing for a number of World Cup coaches after high profile injuries to England's Rooney, Spain's Cesc Fabregas and Frenchman William Gallas in last week's matches.
Alex Ferguson's team have also not beat a German team at home in three attempts in the Champions League knockout stages.
"We have a chance to succeed in Manchester as we are always capable of scoring away from home," said coach Louis van Gaal, who hopes to have Dutch winger Arjen Robben back in the team after he missed the first leg through injury.
