Rumours that Moyes could lose his position at Old Trafford have been rife since his side lost 3-0 to arch rivals Liverpool at Old Trafford on Sunday.
While the majority of the club's support during matchdays have stood by the Scotsman, it appears that the outlook is changing among the United faithful.
"The fans have been very patient," Mitten told BBC Radio 5 live. "I don't think you would get that level of support at any other club in world football.
"Up until a month ago, there was a lot of support for David Moyes but that has changed. I do have a degree of sympathy for him, but there has been under performance across the board at the club. It is clearly a very frustrating time."
United will take on Olympiacos in tonight's crucial last-16 second leg in the Champions League.