Goals from Alejandro Dominguez and Joel Campbell condemned the Red Devils to an embarrassing defeat in Greece, leaving Moyes' side with everything to do in the second leg.
But this season has been full of disappointment, as Moyes has struggled in the Old Trafford hot seat having been given the unenviable task of replacing Sir Alex Ferguson, and is subsequently under pressure from a section of disgruntled United fans.
The home form has been catastrophically bad, with United losing against West Brom, Everton, Newcastle and Swansea, whilst their work in the transfer market has also been poor, failing to show any of the clout that they once exhibited under Ferguson having missed out on a number of key transfer targets.
The blame has been given to a number of sources, from Moyes, to the players not trying and to the previous manager leaving behind a squad incapable of mounting a significant title challenge. With that in mind, who do you believe to be the reason for United's failure this year? Or is it simply a combination of all three?