Speaking on Sky Sports after United's defeat, Keane said: "Overall, I think the game was poor second-half, the expectations at United are so low that everyone's comfortable with a 1-0 defeat.
"It does worry me (that), couple of the new signings, there's a bit of encouragement with that, they get you up the pitch, results will improve - it's always tough against Arsenal.
"But it's another defeat, no goals. There's still that worry, I had it before the match, what we saw, but you never felt like United had two or three goals in them."