The Bluebirds spent big on the Chile midfielder over the summer, with £11million required to lure him away from Sevilla.
Medel's no-nonsense approach is perfectly suited to life in the Premier League and he has quickly become a fans' favourite in South Wales.
Mackay is delighted to have seen his judgement rewarded and has paid tribute to the manner in which Medel has gone about his business on and off the field.
He told Wales Online: "Gary has been outstanding in terms of the way he has adapted to a different culture and settled into Premier League football seamlessly.
"He is having English lessons four times a week and is making good progress, he has been working hard on that.
"Those English lessons take time, but he is enjoying living in this city. He has settled in his house and knows where the better restaurants and shops are. All of that helps a player settle in."
Medel and Cardiff travel to Aston Villa in domestic competition on Saturday, before attention turns to the international break.
With Chile set to face England on 15th November, Mackay is planning a scouting mission to Wembley Stadium to see how one of his charges fares against a Three Lions line-up which will likely include a number of upcoming Premier League opponents.
With fixtures against Manchester United and Arsenal on the horizon, Mackay added: "I'll be there for that one, it's a fixture well worth taking in.
"Cardiff are fortunate to have top international footballers in our squad, and that's great for the club."