The reigning Premier League champions face the division’s bottom side at Old Trafford hoping to bounce back from defeat to Stoke City last time out.
United have already lost eight times in the league this season and Moyes admits three points are crucial for his side on Sunday.
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“I never thought we looked like losing against Cardiff but actually, truthfully, I thought we were better at Stoke. We can improve a lot on both performances.
"All we can do is try to win the next match, To get to the position we want to be in, teams above us will have to slip up. We accept that, but we have to be ready to take the chance if offered. We have always felt ourselves capable of moving up the table."
Following the news that Nemanja Vidic is to leave the club at the end of the season, Moyes admits he is now trying to decide who will take over the armband at Old Trafford.
"Every club needs pressure on the top places. Between now and the end of the season I will be making my mind up about a new captain,” he added.
“The person who takes over as captain of this club has to understand the responsibility it carries, what's required of you. But I think we've got a lot of leaders in the squad. They will all get their chance to stake their claim."