The pair were talking parallel to the 18th green but seperated by a water hazard, but Hendry's club fling - probably intended to land in the drink - cleared the water and landed in the weeds directly behind them.
"Oh my goodness," remarked McOnie, after the pair flinched when the club landed metres behind them.
"What was that??? That was close," exclaimed a puzzled Campbell, as the club was retrieved from the weeds.
The pair continued with the interview, while Hendry made for the exits as his title defence ended on a sour note.
Hendry apologised for the incident when contacted by the Herald on Friday night.
"I'm pretty gutted. I was taking my frustration out on the putter and was attempting to throw it into the pond when it hit some rocks," Hendry said.
"I appreciate it wasn't the most mature or professional reaction, but I feel like I've been playing poorly of late. It was a lapse in judgment, I was trying to win the national open again and it's been a tough period in my game.
"I hope people appreciate the pressure we're under, and the expectations we put on ourselves, but it doesn't excuse letting go of the putter.
"I'm only human, and I'm going through a rough patch on and off the course."
Australian Terry Pilkadaris leads the event at 15-under.