It wouldn't surprise me one bit.
There have been rumbling about his attitude off the pitch before this. The guy who leads Sunday Supplement said that he was building some massive home and adding to his ever growing car collection.
Not that he shouldn't be allowed to spend money on luxury things.
From Rashford's perspective, you can see why he'd be unhappy. He rarely plays through the middle anymore. If he was playing under a manager like Pep, Tuchel or maybe even Klopp, he'd be leading the line. Not playing every game is probably the right call for his career in the long term, but young lads want to play. When you go from being first choice to squad rotation, it's a big change.
The thing is, I never know why managers give debuts to young guys like him if they're not going to keep him in regular contention. It's like when we promoted Macheda. He scored some important goals for us after a run of excellent form for The Reserves. To then expect him to drop down to Reserve level after tasting the heights of the game, must be very difficult. It's hard to motivate yourself at that lower level. We've seen this with Joyce's comments about Januzaj and Wilson. That's why it's so important to give players their debut at the right time.