Kim has been outstanding for the Bluebirds in pre-season, playing just behind the main striker and showing no signs of jet leg from his commitments with South Korea.
"Kim has power and a little bit of X-factor," said Mackay, who has been delighted by the form of his £2m signing from Japanese club Cerezo Osaka a year ago.
"He has played a lot of football over the summer and got through a lot of travelling. We have tried to protect him and he has come through that period.
"Kim reached good levels of performance last season at Championship level and we will be looking for that more and more in the Premier League."