The 37-year-old is bidding to win back-to-back majors at Aronimink Golf Club in southwest Philadelphia and become just the fifth player for 66 years to clinch the first two majors of the year.
He cut his practice round on Tuesday after a few holes, having at one point removed his shoe, battling with a blister on the little toe of his right foot that emerged during last week's Truist Championship.
McIlroy reportedly ripped the nail off earlier this week and was visibly struggling but he completed his planned practice round on Wednesday (Thursday AEST), later telling the BBC that the issue was "a mountain out of a molehill".
"I did feel a little soft having to walk in because of a little toe," added the man who's seeking to emulate Jordan Spieth, who was the last to win the season's opening two majors, then the Masters and US Open, in 2015.
The Northern Irishman seemed in good spirits, raising a laugh as a spectator praised his cameo in the Devil Wears Prada 2 and appears to be moving fine as he sets his sights on a seventh major championship.
He arrived at this tournament last year admitting he lacked motivation, having finally clinched the career grand slam a month earlier with a long-awaited Masters triumph.
This time around, having again triumphed at Augusta, he has a very different mindset and is focused on adding to his major haul – one more would take him past Nick Faldo and make him the most successful European of the modern era.
"Coming into this tournament feels a lot different than what it did last year," he said.
"I feel like I've got some nice clear road ahead to try to get some more of these majors.
"I need to take the time after the Masters to reset and decompress and get myself in the right mental space again to get myself up for this tournament and keep going for the US Open and the Open Championship."
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