They were a Europa League team for a reason. The odds in their favour? Give it a rest. Beating Schalke and Lyon like it's some sort of big accomplishment?
United has spent like 700 million net on the transfer market in the last 5 years. Ajax has spent pennies.
United had 100 million dollar Pogba, 50 mil Martial, 45 mil Mata, 40 million Mkhi off bundesliga player of the year, 35 mil Herrera, 30 mil Bailly, and so on and so forth. United's squad is worth 10x what Ajax's is worth. Ajax didn't even win the sad sack Dutch League last year Ffs.
They're supposed to be running with the big boys, not playing minnows like Ajax in the Europa League. United losing that match would have been appallingly embarrassing given the money they have spent especially alongside finishing 6th in their league.
Odds in Ajax's favour? You have to be taking the piss.