The champions have struggled to adapt to life under Moyes this season, and the Red Devils are currently seventh in the Premier League, 18 points behind leaders Chelsea.
Scholes told Sky Sports News: "It's been difficult for the new manager, he needs time to get to know his players and that's been a big problem.
"He doesn't know his best team yet and they're not performing for him and that makes it even harder for him to find it.
"United have struggled and City are going strong, but we always believe we can win at Old Trafford."
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