Woods missed several easy putts at the AT&T National
Tiger Woods has been interviewed as a witness about his relationship with a doctor charged with injecting athletes with growth hormones.
Woods, who said Dr Anthony Galea treated his injured knee, has denied using any performance-enhancing drugs.
The Canadian has been charged with unlawful distribution of human growth hormone to three unidentified National Football League (NFL) players.
Woods was interviewed by the federal authorities in Florida last week.
The world number one, who is easing his way back on to the US circuit after his much-publicised marital troubles, has not been accused of any misdemeanours and was treated as a witness.
"I co-operated and answered all their questions and that was it," Woods told reporters after the first round of the AT&T National at the Aronimink Golf Club in Pennsylvania.
Woods said Dr Galea treated him with a "blood-spinning" process, where blood is drawn, spun on a centrifuge and then injected into the injured area.
His agent, Mark Steinberg, told the New York Times the golfer was not under investigation.
"It was confirmed that because he did nothing illegal, he is not the subject of any criminal investigation," Steinberg said.
Baseball players Jose Reyes and Carlos Beltran admitted earlier this year they had also been interviewed about their dealings with Dr Galea.
Mary Anne Catalano is likely to give evidence against her former boss
Dr Galea, who is not licensed to practice medicine in the United States, was charged in May with conspiracy, smuggling, unlawful distribution of Human Growth Hormone (HGH) and introducing the unapproved drug Actovegin into interstate commerce.
Last week, his former assistant, Mary Anne Catalano, pleaded guilty to one count of lying to border agents in a plea bargain which may lead to her becoming a crucial prosecution witness against Dr Galea.
Catalano said she agreed to bring vials of drugs, including HGH, into the US for Dr Galea to use on athletes and was told to lie to border agents.
Woods missed several easy putts at the AT&T National in Pennsylvania on Thursday.
He ended the day seven strokes off the pace, trailing joint leaders Australian Jason Day, India's Arjun Atwal and Americans Nick Watney and Joe Ogilvie.
"I just putted awful. It was a frustrating day on the greens, especially how good I was driving it.
"My speed was good but I never hit the ball on line. Even when I hit my putts on the exact line I wanted, they still didn't go in," said Woods.