It's quite reasonable that Real Sociedad is more favored than Manchester United because Real Sociedad will have the advantage of playing at home, and as we know, Man United has inconsistent performance. But still, that doesn't rule out the fact that Man United could still make a surprise, because even though they are in ruins in the league, but what is happening in the Europa League is the opposite, where Man United can perform well and they get to the last 16 without having to go through the play-offs.
But for me Manchester United will try their best in the European league to win even though the opponents they face are quite strong but I am sure they will show their best game. In addition, Manchester United only have one chance for them to penetrate the Champions League so Amorim must take advantage of the European League as best as possible to win both legs in the last 16.
Real Sociedad is indeed a strong opponent but in the statistics of the meeting where Manchester United managed to win two wins when facing Sociedad so there is good capital for the Amorim squad to steal a victory in the first leg. But Manchester United's shortcomings of course they do not have a qualified striker and their defense line is also not strong enough.
I strongly believe that the game would going to be a very though match Manchester united. because their performance now is not encouraging at all, and even though they are playing at away and also their head to head games shows that both teams performances are quite the same. So with that I think the game may likely end in draw because both of them are almost equal even in their leagues tables.