Actually for Bayern from the 5th match they are also safe so they are not too eager to get 3 points in the previous match because after all they need to save energy for matches that are not too important.
You are right because with the points Bayern Munich have right now there focus is not much on there match against Manchester United because they will like to reserve most of there key players so that they will have enough energy to perform well on there next round, so that will make them use there younger players against Manchester United.
So however if Manchester United utilizes the opportunity and win Bayern Munich they could stand a bit chance of hopping for the second position if Galatasaray and Copenhagen plays draw.