The Mexican scored the only goal of the game, as the Premier League champions edged out rivals Liverpool 1-0 in the third round of the competition on Wednesday.
United have only netted seven goals in five league games so far this season, and Moyes admits that Hernandez's display has presented him with a dilemma.
"Everybody tells me about the goals he scores and I saw one tonight," Moyes told the media. "They tell me he always gets his goals throughout the season and if he keeps doing that it gives you problems.
"We've got good strikers here but we need pressure and we need goals. We need to keep scoring goals."