Dustin Johnson Insinuates Sex With Paulina Gretzky Caused Back Injury

No, Dustin Johnson didn't hurt his back earlier this year swinging a club -- instead, he strongly insinuated Wednesday it was a different kind of stroke that caused the injury.

Johnson was out in New York getting ready for the PGA Championship at Oak Hill Country Club when he was peppered with a few questions about the muscle pull that yanked him from the Saudi International golf tournament back in February.

The 38-year-old former Masters champ didn't explain fully what caused the problem ... but he sure hinted it had something to do with fooling around with his wife, Paulina Gretzky.

Check out video of the exchange with a reporter ... when the media member asked the LIV star if he had gotten hurt playing golf or "lifting up" one of his children -- Johnson broke out a huge, wry grin.

"Yeah, lifting up a kid," he said, stifling a laugh. "Just a bigger kid."

The remark left the room full of journalists in stitches ... and the ear-to-ear smile that Johnson continued to wear didn't require any further follow-ups.

Of course, Johnson could've been talking about something completely different ... but both he and Paulina have had all day to clarify the comments -- yet the two have remained tight-lipped.