McKibbin, who shared a warm embrace with McIlroy after securing a PGA Tour card at the end of last season, looks poised to joined the Legion XIII team of Jon Rahm and Tyrrell Hatton in the Saudi-funded breakaway league.
The 22-year-old honed his game at the same club in Northern Ireland as McIlroy and rang the four-time major winner for advice about the potentially lucrative switch.
"I have known Tom since he was 10, 11 years old, and as soon as he got the offer, he rang me," McIlroy said ahead of his title defence in the Dubai Desert Classic.
"I had just landed in New Zealand. We had a really good conversation and I talked to him multiple times over the course of December to sort of get a feel for what he was thinking and what he was going to do. And all I could do is give my perspective.
"I really like Tom as a person, as a player. I think he's got a ton of potential. I said to him, 'if I were in your shoes, I would make a different choice than the one you're thinking of making'.
"Working so hard to get your Tour card in the States, something that he did, to achieve that goal last year was a big achievement.
"I think what he potentially is sacrificing and giving up with access to majors, potential Ryder Cup spot ... if I were in his position and I had his potential, which I think I have been before, I wouldn't make that decision.
"But I'm not him. I'm not in his shoes. He's a grown man at this point and can make his own decisions. All I can do is try to give him my perspective.
"Personally for me, it would be a little disappointing if it were to happen but again, I made it perfectly clear: I am not going to stand your way if you need to make the decision you feel like you need to make for yourself.
"But at the same time, I feel like he's giving up a lot to not really benefit that much.
"I think we all see the potential that he has and I definitely think he can be a top-10 player in the world. But his ranking won't show that for the next couple of years if he makes one decision over another.
"No-one knows exactly how much he's going to get (for joining LIV). What I would say is, there is still a ton of money to be made on the PGA Tour and the DP World (European) Tour.
"There is so much money in the game and some would argue too much money in the game for the eyeballs that we attract. For whatever the benefit may be, I don't think it's worth the sacrifice to what he's potentially going to give up."
McKibbin turned professional in April 2021 and won his first European Tour event in June 2023 at the European Open in Germany.
He declined to comment on the possible move during last week's Team Cup in Abu Dhabi, where he helped GB&I to a resounding victory over Continental Europe.
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