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.
Forget about Real Sociedad playing at their home ground because despite some mistakes that Manchester United made in their Europa League matches but they were still good to reach this knockout round playoffs so i think Amorim have a better plan for Manchester United and won't allow Real Sociedad to cut short their dream of moving forward to the next stages of the Europa League. Manchester United lacks ability to arrange their selves very well in their Europa League games but since they could win Rangers and FCSB in their last 2 Europa Leagues games, there is tendency that they can also face Real Sociedad without fear of defeat despite that Real Sociedad is stronger than the last two opponents Manchester United met. I know that Manchester United has not been performing as expected but i still wish them to advance to the next stages since they are a team from England.