McIlroy felt muscle spasms in his lower back at the Arnold Palmer Invitational that forced him to withdraw before the third round. He had hoped to be at the TPC Sawgrass sooner, but his recovery went slower than he thought it would.
"It's better than it was," the Northern Irishman said on Wednesday (Thursday AEDT).
"I couldn't stand to address the ball on Saturday morning on the range at Bay Hill, and it's obviously better than that. So, yeah, probably a game-time decision, but all indications are pointing in the right direction."
McIlroy went to the back of the practice range at the TPC Sawgrass and hit shots up to the six-iron and said he felt OK, describing the area in his lower back as more sensitive than any pain.
He then took a putter and wedges to chip and putt on the back nine ahead of the first round.
McIlroy didn't feel the need for a full practice round at a course where he has won twice, most recently his playoff victory over JJ Spaun last year.
The last defending champion who didn't return to The Players was Australian Cameron Smith in 2023 because of his decision to join the Saudi-backed LIV Golf circuit.
And the last defending champion who didn't play because of injury was Tiger Woods in 2014 after having the first of what would be seven back surgeries.
Five Australians are in the field for the $US25 million ($A35 million) showpiece: Adam Scott, Jason Day, Min Woo Lee, Cam Davis and Karl Vilips.
