PITTSFORD, N.Y. – Rory McIlroy’s post-round press conference Tuesday was decidedly subdued and the Northern Irishman explained following his opening 1-over 71 at the PGA Championship that he’s been battling an illness.

“I'm fighting something. I thought I got a great night's sleep last night, and I look at my Whoop, and I was 22 percent recovery, and my skin temperature was 3.5 degrees higher than what it's been. I'm fighting something,” McIlroy said. “I actually feel better today than I felt yesterday, so plenty of water and a bit of rest, I'll be fine.”

Whoop's website states that for anything below 33% recovery, "Rest is likely what your body needs. It is working hard to recover, potentially from overtraining, sickness, stress, lack of sleep, or other lifestyle factors.”

It may be illness that has slowed McIlroy but there was also plenty of stress Thursday at Oak Hill, where he began his round at No. 10 and bogeyed the 15^th, 17^th and 18^th holes to turn in 3 over.

“Just not at my best. I'm just struggling with my swing. It's pretty messy out there, so just trying to make pars,” he said. “It was tough as well. There was a lot of crosswinds off tees, so it made it hard to hit fairways.”

McIlroy rebounded on his second nine, starting with a 36-footer from behind the green for par at the second hole. He added birdies at Nos. 3, 4 and 8. Still, it was another middling round following his missed cut at the Masters and his tie for 47^th two weeks ago at the Wells Fargo Championship.

“I take it hole-by-hole,” McIlroy said when asked if he was prepared for what’s shaping up to be the year’s most demanding test.