The column inches have stacked up for the 22-year-old McIlroy since he cruised to his first major title by winning the U.S. Open at Congressional by eight shots last month.
Many have predicted a new era of dominance from the Northern Irishman, filling the void left by the injury-plagued Tiger Woods, but Nicklaus sounded a note of caution ahead of next week's British Open at Sandwich.
"Don't anoint him as the crown prince yet," Nicklaus told the BBC on Sunday. "He has won one major. When he starts to win two, three or four, then you can say he's the guy we've got to watch, period.
"But until that time comes, he's one of a group of talented players that have got an opportunity to win."
Not only has the No. 4-ranked McIlroy won just one major, he has only captured three tournaments in his young professional career.
Nicklaus, the record 18-time major winner, expects that tally to soar.
"I think Rory will add a lot of majors," Nicklaus said. "Rory is a very talented young man who's been a factor in every one of the majors over the last year.
"He could have won the Masters and (last year's) U.S. Open, he could have won the British Open last year. He's a talented young man we're going to see on the scene for a long time."
While McIlroy heads to Royal St. George's as the outright favorite with the British bookmakers to land the year's third major, Woods is resting up after failing to recover from injuries to his left knee and Achilles' tendon.
It has been nearly two months since Woods last played -- he withdrew after nine holes from The Players Championship in mid-May -- and has slipped to No. 17 in the world. He is without a tournament win since 2009 and the chances of increasing his tally of 14 majors to challenge Nicklaus' record haul are fading.
But Nicklaus says there's life in his 35-year-old countryman yet.
"He's a very determined and talented young man, and I think he's determined to get himself healthy," he said. "He's still plenty young enough to play a lot of good golf. I think you'll see a lot from Tiger.
"Whether he overhauls my record or not, it will be interesting to watch."