As if Rory McIlroy's stunning form was not enough to give the American Ryder Cup captain Tom Watson reason to worry, his hopes of victory at Gleneagles next month have been further undermined by a mounting injury list to his American charges.
Jason Dufner was forced to abort his US PGA Championship title defence after 10 holes late on Thursday during the opening round here in Louisville, withdrawing from the event because of a lingering neck injury.
Dufner has been severely hampered by two bulging discs in his neck since April and was eight over par for the day, having triple-bogeyed the par-five 10th, when he decided to pull out of the year's final major.
He shook hands with his playing partners, fellow American Keegan Bradley and South Korean Yang Yong-eun, who are both former PGA Championship winners.
Dufner had to severely limit his preparation for the tournament after having an epidural and being advised by doctors to take as much rest as possible.
"They like you to rest seven to 10 days after that," he told reporters on the eve of the PGA Championship.
"I haven't really been able to do that, so I'm trying to rest, keep my reps (repetitions of exercises) down. I feel sore. I get a little fatigued quicker than usual.
"It's an arthritic, degenerative issue that I'm probably going to be dealing with for a good bit. It's just something that's not going to change. I'm going to have to deal with it."
Dufner, who has been troubled by the injury since the Masters in April, said he would not be healthy until he was able to take a break from the game of six to eight weeks.
"I'm not sure when that's going to be, but I'll get through," the 37-year-old said. "I had obvious reasons for playing; defending (the title) is pretty important to me."
Dufner won his first major with a two-shot victory in last year's PGA Championship at Oak Hill.
After pulling out of the tournament Dufner said: "I've been feeling pretty bad all week. I felt bad last week. I haven't made a birdie in 45 holes and I'm just not able to play golf right now.
"I don't need to be out here. I tried to do what I could, but it is just pointless."
Asked when he might be able to compete again, Dufner added: "It could be two weeks, it could be next year."
Which cannot fill Watson with hope.
Watson also saw Matt Kuchar withdraw from competition on the eve of the the tournament due to a back problem.
Kuchar is the world No 6 and a sure-fire Ryder Cup player for the Americans. Add in Tiger Woods' erratic form and troublesome back and Dustin Johnson's decision to take time out of golf for an unspecified reason and things could not be much bleaker for the American team.