The Hammers were found lacking in the attacking third as they went down 2-1 at the Etihad.
When asked if he was concerned by the form of his forwards, Moyes said: "Yes I am, I've told them.
"I think that we need to be better in that area. We've had opportunities and when you get to the top end you have to have forwards who individually can beat players, make goals and create chances and be clean with the chances, we haven't been in recent games.
"I go back to Europe, we won in midweek but I thought our attacking play could have been much cleaner with our chances."
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