World number three Jason Day said his back proved troublesome during the first round of The Barclays.
Day - playing for the first time since claiming the US PGA Championship at Whistling Straits - did not play Wednesday's pro-am event after tweaking his back.
An MRI cleared Day of any serious injury but the Australian still struggled at the FedExCup play-off opener, despite carding a two-under-par 68 in New Jersey on Thursday.
"I think if I had another day's rest I'd be fine but just coming back today trying to go at it a little hard with the driver definitely hurt," said Day - second behind Jordan Spieth in the FedExCup standings.
"With my swing with how quick everything goes, it kind of crunches down on - the facet joint crunches down on the disc at certain points, and once I felt that at the top of the swing, then just everything kind of fell off balance and hooked it.
"There were a couple of swings out there that hurt. That one on 16 after that marvellous pitch shot definitely hurt. But once everything started heating up the back kind of loosened up a little bit which was nice.
"Structurally I'm a lot fitter and better than I was last year so all the work that I've been putting in to the gym has been paying off. Really trying to push that disc back in."
Day has been hampered by various ailments over the past few years, namely a longstanding disc issue, as well as vertigo.
The 27-year-old's latest injury came about when he was moving a box on Tuesday.
Day added: "It's a little disappointing because I shouldn't have been doing what I was doing, just moving stuff around.
"But you know, I feel like I'm young and I feel like I can - sometimes you feel like you're invincible. You've got to understand that you don't need to be doing that stuff. It's a little frustrating and disappointing on my behalf, just to really understand that I wanted to come into this week fully prepared.
"Yesterday was going to be a practice round for me, and I was a little disappointed because I didn't see the course until today. But you know you've just got to take it as it is and understand you shouldn't be moving stuff under your bus and just be careful next time."