McIlroy told reporters during The Players Championship that he was having the MRI to determine the cause of the back pain he suffered during the tournament.
However, scans have shown that the pain he felt at Sawgrass was a "low-grade response" to his previous injury and is not set to keep him out for any length of time.
Rory McIlroy will have an MRI scan on a back injury next week after confirming the problem still troubled him during the second round of the Players Championship.
"I took three weeks off and then I went back at it again on Friday and instead of maybe gradually building it up again, I hit balls for four or five hours on Friday and did the same on Saturday", said McIlroy, who got married on April 22.
The world's No. 3 player and recent newlywed said he re-aggravated a rib injury in his upper right back that sidelined him for almost two months. The player spent nearly five hours hitting balls on the range that day.More news: Coroner: Teen had healthy heart before caffeine
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Now McIlroy fears he will miss the BMW PGA and where he reigned supreme in 2014.
By close of play McIlroy's even-par aggregate was nine adrift of the leaders, Kyle Stanley and Louis Oosthuizen.
Rahm is looking to become just the third player to win the Players in his first try, joining Hal Sutton (1983) and Craig Perks (2002). "But I scrambled pretty well, and I birdied two of the last three holes to make it somewhat respectable". "I have good momentum going into the weekend", Rahm said.
"To come back to this golf course that we know how challenging it is, it's maybe not the best thing, but it is the way we planned it and we live with it".
Willett followed an opening 79 with a 40 during his first nine holes Friday.