The Chile midfielder was outstanding in the derby win over Swansea City.
Mackay, who takes his side to Aston Villa this afternoon, said: "His pass completion was above 96 per cent against Swansea and he had 99 per cent against Fulham. I don't know that I've ever seen that before.
"We did a lot of reports on him, spoke to various people, and when you've got Xavi coming out in the press saying that he thinks Barcelona should sign him, that's not a bad marker to have.
"Players that keep the ball for the team are gold.
"When I looked at a press cutting after he scored the winner for Chile in the final game to put them through to the World Cup, there was a photo of the three top players.
"One was Alexis Sanchez of Barcelona, the second Arturo Vidal of Juventus and the third was Gary Medel of Cardiff. The photo had those three names and those three teams underneath, which is a bit surreal."
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