McIlroy, 25, has three Major championships to his name and has been in sensational form in winning back-to-back tournaments at the Open Championship and the WGC event at Firestone last weekend.
Tiger Woods, who has been stuck on 14 Majors since 2008, was widely tipped as the man to break Nicklaus' record of 18, but the Golden Bear says it could be the Northern Irishman who eventually achieves it.
"I think Rory is an unbelievable talent," said Nicklaus ahead of the final Major of the year at a Valhalla course he designed.
"I love his swing, I love his rhythm, I love his moxie. He's got a little swagger there, it's a little bit cocky, but not offensive. I like that.
"I like the self-confidence in a young man, while he's got an unbelievable amount of speed in his golf swing and obviously hits the ball a heck of a long way. He also hits it in there constantly, and I admire how he controls it.
"It depends on what he feels his priorities are – and that's his call – but I think Rory has an opportunity to win 15 or 20 Majors or whatever he wants to do if he wants to keep playing. Yet you just don't know what the guy's priorities are going to be in life 10 years from now."
McIlroy goes in to the US PGA Championship as the clear 5/1 favourite to win. The next player in the betting, Adam Scott, is more than double the odds at 12/1.
Woods, who goes into the tournament with concerns over his back and limited preparation time, is available at an unprecedentedly large 50/1 with some bookmakers.
McIlroy is aiming to become just the fifth golfer since 1980 to win three tour events in a row, after Tom Watson, Woods (multiple times), David Duval and Vijay Singh, and he tried to play down the hype earlier this week when he was asked if the "era of Rory" had well and truly begun.
"I don't really know how to answer that," he said.
"Yeah, of course, I've heard it and I've read it. Sometimes I feel that people are too quick to jump to conclusions and jump on the bandwagon and jump on certain things.
"I've had a great run of golf and I've played well over the past few months. Look, I said at the start of the year that golf was looking for someone to put their hand up and sort of become one of the dominant players in the game. I felt like I had the ability to do that, and it's just nice to be able to win a few tournaments and get back to where I feel like I should be.
"So I'm not necessarily sure you can call that an era or the start of an era, but I'm just really happy with where my game is at the minute and I just want to try and continue that for as long as possible. … If you read everything that was being written, I'd turn up at the first tee on Thursday thinking I'd already won the tournament."
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