Matt Kuchar battled dizziness and spells of weakness as he carded a one-under 71 in the opening round of the Canadian Open.
Kuchar, who was runner-up to Jordan Spieth at The Open last week, mixed four birdies with a bogey and a double bogey at Glen Abbey Golf Club.
"I had a couple of spells where I got a little bit dizzy and I felt weak. I don't know where it came from," Kuchar told a news conference.
"I've had plenty of time to get over the travel. Hopefully it's just something that passes real quick."
Kuchar said he had never experienced it before, adding it had no impact on his play.
"I shook it off the couple times it happened. No, it didn't affect," he said.
Hudson Swafford, Brandon Hagy, Kevin Chappell, Matt Every and Ollie Schniederjans lead at seven under.