Herrera almost joined United ahead of the 2012-13 campaign but the deal collapsed and he eventually moved to Old Trafford from Athletic Bilbao on a four-year deal last month.
The 24-year-old put in an impressive showing in a 7-0 demolition of Los Angeles Galaxy in his first outing for the club, while he also started the 3-2 win over Roma on Saturday.
And Mata - who joined United from Chelsea in January - believes his fellow Spaniard can put his stamp on England's top flight this season.
"He is a very, very good midfielder," Mata is quoted as saying by the British media.
"He's a good guy, my friend, and we've known each other since we were 15. He's top quality, he can play quick, slow and dictate the rhythm of a game.
"He can score as well. He's a very complete midfielder and can bring these qualities to the team. I enjoy playing with quality players like him and Wayne Rooney. We try to play the same way."
Mata is also enjoying life under manager Louis van Gaal and believes the Dutchman's high expectations can only be good for United.
He added: "He is very honest with the players, he says what he thinks and has a clear way of understanding football.
"We feel the manager is a great manager who has brought a strong mentality. This club is made for a winning mentality and I think he has it.
"He has had success in different countries. We are happy with him and the way he works. Everything is new but we are adapting well to his style of football.
"He is right to be demanding. As a player you want a coach like this, always demanding more and to play better and try to win the games earlier or in a different way."
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