The champions currently trail league leaders Chelsea by 16 points, and sit nine points off a Champions League qualification spot, but the Scot insists he is "doing the right job"
The Premier League champions sit seventh in the table, nine points behind fourth-placed Liverpool and 16 adrift of Chelsea having lost eight of 25 league games.
But, ahead of a difficult trip to title contenders Arsenal on Wednesday, Moyes insisted criticism of his management has not affected his approach.
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"It was always going to take time. There is rebuilding going on year after year here, and we will continue to try to do that.
"I just keep doing the job because I know that we’re doing the right job. We’ll do the same things, we’ll make sure things are right - prepare the players well and things will change I have no doubt."
Moyes' side are 21 points worse off than they were after 25 games last season, and the Scot suggested that demonstrates how far United's rivals have come.
"The improvement in the teams in the Premier League has been big," Moyes said. "There have been a lot of improvements from sides in the Premier League and obviously we’ve not done as well as we did last year.
"I think there are certain different reasons for it, I don’t think there’s any particular one. I think there’s a combination of different things - the change of manager being one of them. But lots of other things as well.
"We’re trying to see how our results have not been as good as they have been. They should be, and we will continue to look at that. There’s no one person or one thing [to blame]."
Moyes also defended his players and thanked United fans for the backing he has received since taking over at the club.
"I think the players are doing great. I think I’ve got a great group of players. I’m very fortunate I took over the champions and I think the players have been terrific," he added.
"The supporters have been fantastic. That’s why the right clubs, pick the right managers and the right managers pick the right clubs. You pick clubs where you know is the right place for you.
"That’s why I always hoped and dreamed that Manchester United would come for me - and they did in the end."