Mata has already trained with his new teammates and will make his debut tonight against Cardiff City.
"We’ve had a problem at Old Trafford of making and scoring goals," said Moyes. "That’s been our biggest downfall.
"It’s not necessarily been about conceding goals or how we’ve been away from home. It’s just that, when we’ve been at Old Trafford, we’ve tended not to be as clinical or make as many opportunities as we would have liked.
"With Juan, one or two of the players have said to me, 'What a great signing, we can’t wait to play with him'. From what I’ve seen with him in training — and it’s only been a couple of days — I’m pleased we’ve got him.
"I have been without Wayne Rooney for about a month, Robin (van Persie) for two months, and I think, if I’d had Juan in that period, I’d more than likely have had better results."
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