The beleaguered Scot spent Monday locked away with his back room team while several of his most senior players were understood to have been mocking his perilous situation.
Moyes' standing reached a new low Sunday after the champions were humiliated by Liverpool at Old Trafford. Two penalties from Steven Gerrard and a late Luis Suarez strike condemned United to its ninth loss of the league campaign and left it a staggering 14 points adrift of fourth-placed Manchester City, which has two games in hand, and Champions League qualification.
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But while the former Everton manager was attempting to devise a plan that would help see his side overturn a 2-0 first-leg deficit against the Greek champions, several of Moyes' most senior players were ridiculing his plight and suggesting his days were numbered regardless of the result.
A source told Goal: "We've never seen this level of contempt for anyone at the club in the past, let alone the manager."
Moyes has presided over a wretched season which has seen his side go out of both domestic cup competitions against teams currently among the bottom six in the top flight, while United's league campaign is now restricted to scrapping with his old club for a Europa League place.
The Scot has spent close to 65 million pounds on two new players, Marouane Fellaini and Juan Mata, both of whom have struggled to make any sort of positive impression since moving to Old Trafford.
Indeed, both expensive signings failed to complete the 90 minutes against Liverpool, after which Moyes admitted he was finding the job of succeeding Sir Alex Ferguson "harder" than he had anticipated.
The fixture list, however, does not afford Moyes any semblance of respite. After United hosts Olympiakos on Wednesday it then travels to West Ham on Saturday evening before the Manchester derby against City the following Wednesday.