The Chile international has quickly shown his class in the opening rounds of the season.
"He is one of the best signings this club will ever make," Mackay told the Western Mail.
"I don't think that's over dramatic.
"He has been two minutes in the door, a Spanish speaker with limited English and yet he has taken to our club like a duck to water. There is a confidence about him - an aura which underlines he deserves to be playing Premier League football.
"He is a natural leader and as his English gets better he will develop even more. He settled immediately and gained immediate respect from all players."
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