Mata is expected to sign for United today in a club record £37 million deal.
Meulensteen said: "I think he's a great player.
"I think he would definitely improve them."
Former Reds coach Meulensteen added: "In the past United didn't really have such as an interest in players as they have for Mata and obviously he's available.
"Player wants to come, Manchester United want him, simple."
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