United broke their transfer record to land Mata from Chelsea in a £37.1m deal and his arrival has eased the pressure on Moyes.
But the United boss admits there is still a long way to go before he can lure other big-name signings and make the team a world force again.
"We need to give Juan Mata time to settle in.
"But I feel as if it's still a big job. If I could have got another player in then great, but it wasn't the case and I want to make the right signings if I can and get people in who will make a real difference."
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