Giggs, who turns 40 next week, has never faced Cardiff during his illustrious 22-year career at Manchester United, and the Bluebirds will become his 117th different opponents as a Red Devils player should he take the field.
Player-coach Giggs, who won 64 caps for his country, was born in the Welsh capital, and Mackay admits it will be special to see the veteran make his return.
"Every day of the week, every week of the year for the last 15 years he has been a top player," said Mackay.
"He is a top bloke and he is probably my favourite player of the last 15 years.
"I met him a couple of weeks ago at the FA Pro Licence course I was talking at, and he is now stepping into the other side of the game in that player-coach role I had at one point and a lot of players have had at some point when their careers are finishing.
"But I think you look at how he has conducted himself professionally through his whole career and he just looks a model pro.
"The way he has kept his body and how his game changed when his pace went, and his thought process in terms of how to play.
"Even the way he started to adapt his body through using yoga to allow him to play into his 40s, he has been an absolute star and he is obviously an iconic figure here for what he has done for Wales and I have no doubt at one point he will end up in management.
"He has learned from the best (Sir Alex Ferguson) and it will be good to see him on Sunday."
Mackay is also acquainted with United boss David Moyes, having been invited to spend a few days at Everton as part of his own coaching qualifications.
And he has no doubt United, who have shown signs of returning to their best form over the course of the last month, have got the right man to replace Ferguson, and deal with the pressures that go with it.
"Fifteen Scottish coaches and managers spent the weekend with him at Everton," he said. "We watched the game and were invited to training and had a couple of hours Q&A session with him which was private, enclosed, but very open and honest.
"He was absolutely fantastic. I couldn't get enough of it. The way he carried himself, spoke passionately about football and about management.
"It was something I really took a lot of things from and was honoured and humbled he allowed us the access and the openness to him.
"It was a private discussion and he was honest about how he'd dealt with situations during his time at Everton.
"It was a little insight into a top manager at the time who has gone on to take one of the biggest jobs in the world.
"He has gone into a well-oiled machine, let's not kid ourselves, he has gone into something that wasn't broken.
"But reading Sir Alex's book, when they talked about him sitting down with the Glazers and David Gill to discuss the future manager, certain criteria was needed and I think they have absolutely got that in David Moyes in terms of a long-term strategy and a man they feel is beholden to the title of Manchester United for a long time.
"Over time the team will adapt to the way he wants it.
"He is in the door two minutes but, at Manchester United, you have to win. It doesn't matter about settling in time, you have to win."