The forward has found it tough going since he made the shock decision to quit Arsenal for Old Trafford back in January, snubbing Pep Guardiola and Manchester City in the process.
Sanchez lost the ball an incredible 33 times during Monday's roaring 3-2 comeback win at Crystal Palace, with the Chilean also clearly irked by the inability of some of his new team-mates to find him with passes.
The 29-year-old has scored just once and boss Jose Mourinho is yet to find the right formula to get the best out of his attacking attributes for United.
Sanchez has been putting the effort in on the training ground, playing catch-up in terms of his overall fitness, staying behind for extra sessions.
United insiders, however, have also observed in recent training drills how 'demanding' he can be and is often seen gesticulating when something simple doesn't come off.
The South American is a likeable character behind the scenes and staff are putting down his apparent frustration and mixed form down to trying too hard to impress his new employers.