Not long ago, Tottenham and United were the tournament favourites, but apparently their "successes" in the Premier League forced the bookmakers to make their odds more reasonable. I don't know if Sociedad and AZ can knock them out, but I believe in Sociedad more. United had a grueling game with Arsenal, so maybe they won't have time to refocus on the Europa League. Besides, the overall result against Arsenal is positive, so it is difficult to expect United to show two positive results in a row 
Keep focusing on the bookmakers, they're not always right for real. Az will have to sit back, contain Tottenham Hotspur and hit them with counter attacks otherwise they'll be gone on Thursday night if they decide to come all out against Tottenham Hotspur away from home. Anything can happen, they have a chance to qualify if they can just defend the goals they'll score. I'm positive Manchester United will wrap things up against Real Sociedad, they won't struggle to get the win.. bias aside, they have what it takes to win this. Winning the Europa League Competition is the best shot they have so they could qualify for the Champions league. They are going all in for this shiiit.
Bookmakers are currently quoting this game as follows:
1.86 - 3.35 - 4.80
United are favourites, but they are a small favourite, with their chances of winning in regular time just over 50%. It makes sense that 14th place in the Premier League is still stronger than 11th place in La Liga, but we have seen United fail in even more obvious games on more than one occasion this season.