Spieth, who won The Open on Sunday, is bidding to become only the sixth player to win all four Majors at the US PGA at Quail Hollow in North Carolina in two weeks’ time.
McIlroy has been one Major away from doing the same thing, with only the Masters and the Green Jacket that goes with it evading him so far.
And the Northern Irishman has admitted he is a “big fan” of McGregor and tries to follow him in the confidence and belief that he has in himself.
“Jordan’s finish was unbelievable,” he said. “What he did was seriously impressive and Matt Kuchar must have felt like a train hit him. It went from being close to being out of sight so quickly.
“But to be successful you have to have defiance. Look at Conor McGregor – and I'm a big fan. People see this trash-talking whatever but his mentality and his belief in himself is just unbelievable.
“If you believe 100 per cent in what you’re doing, if you have that conviction, you can do anything.”
McIlory wants to get to the career Grand Slam before Spieth and has insisted that not only is it his main motivation now, but that it would hurt desperately if his American rival was to achieve the feat first.
“Am I motivated by getting there first? I really am,” McIlroy added. “I do not want Jordan getting that Grand Slam before I do.
“Look, he is a great guy, but it would hurt a lot if he did it first. Phil Mickelson and me are the two players in the last few years who have had the chance to do the Slam.
“For Jordan to come in ahead of both of us and swipe it away would be tough to take so I desperately want to win the PGA (to stop him winning it).”
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