The Chilean midfielder joined the Bluebirds for a club-record £11m from Sevilla in August.
Despite some concerns over whether Medel would settle in at Cardiff, Mackay has revealed that the 26-year-old is enjoying life in the top flight.
"Gary has been outstanding in terms of the way he has adapted to a different culture and settled into Premier League football seamlessly," the Scot told Wales Online.
"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 has made 10 appearances for Cardiff so far this season.