Two days after playing down concerns over his fitness, Tiger Woods was forced to withdraw from The Northern Trust ahead of his second round at Liberty National.
Woods struggled to an opening four-over-par 75 on Thursday after restricting himself to chipping and putting on the back nine of Wednesday's pro-am due to stiffness in his back.
In a statement released on Friday, the Masters champion wrote: "Due to a mild oblique strain that led to pain and stiffness, I have to withdraw from The Northern Trust.
"I went for treatment early Friday morning but unfortunately I'm still unable to compete. I'd like to thank the New Jersey and New York fans for their support and remain hopeful I can compete next week at the BMW Championship."
Speaking on Wednesday, Woods said he felt it was the "smart" approach not to hit full shots during the second half of the 18-hole pro-am, adding: "This is kind of how it is. Some days I'm stiffer than others."
The 43-year-old has played just 13 tournament rounds since winning his 15th major title at Augusta National in April, two years after he underwent career-saving spinal fusion surgery.
Woods followed a missed cut in the US PGA Championship with a top-10 finish in the Memorial Tournament and a tie for 21st in the US Open, but then took a month off before missing the cut in the Open Championship.
Speaking at Royal Portrush, Woods admitted he had little choice but to play a limited schedule.
"Getting myself into position to win the Masters, it took a lot out of me," said Woods, who has had four knee operations and four back surgeries during his illustrious career.
"I want to play here as long as I possibly can and you have to understand if I play a lot, I won't be out here that long."
Woods is projected to fall from 28th in the FedEx Cup standings to 34th and would therefore need a good performance in the BMW Championship, if he is fit enough to play, to climb back inside the top 30 and qualify for the Tour Championship.
The former world number one is the defending champion in Atlanta after beating Billy Horschel by two shots at East Lake for his first victory since 2013.
Woods flew straight from Atlanta to Paris for the Ryder Cup but looked fatigued and failed to win a single point as the United States were easily beaten by Europe at Le Golf National.
He returned to action in the Hero World Challenge in December and enjoyed a consistent start to 2019 before his emotional Masters triumph, 11 years after his last major title in the 2008 US Open.
Friday's withdrawal will inevitably prompt speculation that the Masters represented the last hurrah of a remarkable career, but Woods will be determined to prove the doubters wrong once more and resume his pursuit of Jack Nicklaus' record of 18 major titles.