The problem arose after a therapist had applied hot oils, normally only used on Woods’ injury-prone lower back, to his neck, causing it to heat up. Woods was seen pressing a water bottle against his neck before going on to hit three-under at TPC Boston.
“I had put some pretty hot oils on there,” he later told reporters. “My lower back’s used to it, it’s accustomed to it, we do it all the time so I can get loose. But I decided to put some up on my neck. It’s not as tolerant as my lower back.
“The whole idea is to keep my spine loose, my spine’s not what it used to be and never will be.”
Woods finished the day four shots off leaders Harris English, Kevin Streelman, Cameron Davis and Russell Henley in a congested leaderboard.
Playing his third tournament since the PGA Tour resumed, Woods had reverted to his usual putter he had rested for the PGA Championship where he finished tied for 37th on three under.
He hit his first birdie on the par-5 18th, but went on to card four more birdies over the next six holes before bogeying the ninth as he headed to the clubhouse in Massachusetts.
“For me I really haven’t played so this is nice to come out here and compete again, get another competitive round under my belt,” Woods told GolfTV.
“I wish I would have hit the ball a bit better today, I just did not drive it very well and only hit a few good iron shots in there.
“But when I did put it in there I made all the putts. I need to give myself more and more looks at it.”
This week’s Northern Trust forms part of the PGA Tour’s FedEx Cup playoffs with players vying to make the Tour Championship, which Woods won in 2018, in Atlanta ahead of the US Open later in September.
The top 70 players will qualify for the next stage of the playoffs which begin next week at the BMW Championship in Illinois.
Justin Thomas, who finished alongside Woods on three-under on Thursday, currently leads the FedEx Cup standings ahead of PGA Championship winner Collin Morikawa.