Brooks Koepka hit out at Patrick Reed in a blunt assessment of the notorious bunker controversy that blighted the Hero World Challenge in December.
Reed received a two-stroke penalty for improving his lie when he moved sand behind his ball with his practice swing during the second round in the Bahamas, although he denied accusations of cheating, most notably from Presidents Cup opponent Cameron Smith.
Koepka pulled no punches when asked about the incident and accused Reed of "building sandcastles", while the world No 2 also claimed that cheating in professional golf "goes on a little bit more than people think".
The hard-hitting interview with the four-time major champion was published on SiriusXM's YouTube channel on Tuesday during a media day to promote the PGA Championship at Harding Park, where Koepka will bid for a third consecutive victory in the event.
When asked if Reed's actions could be construed as cheating, Koepka said: "Yeah. I don't know what he was doing, building sandcastles in the sand.
"But you know where your club is. I took three months off and I can promise you I know if I touch sand. If you look at the video, obviously he grazes the sand twice and then he still chops down on it."
Koepka also revealed that he witnessed one of his playing partners improving his lie in the rough during a US Open, although he did not give a clue as to who or when, and added: "It goes on a little bit more than people think.
"I've been guilty of it. I haven't opened my mouth. But now if I saw it, just because of where I'm at in the game, the stature that I have, I would definitely say something."
Koepka again reiterated that there was "no rivalry" between himself and Rory McIlroy, who ended the American's 37-week reign at the top of the world rankings last week, and that he is merely focused on getting his game back on track following his three-month period out of action with a knee injury towards the end of last year.
"We haven't competed going into a major coming down the stretch," he said of his battle for world No 1 with McIlroy. "I think the only time we really competed with each other was the WGC.
"So other than that, we haven't been in contention in the same tournaments coming down the stretch, so it's hard to say there's a rivalry. Even people talk about the Phil and Tiger rivalry, it was kind of one-sided there for a long time, too. I just don't see rivalries in golf, I really don't.
"I've just got to play good golf, that's all I've got to do. If I play good golf, everything should take care of itself. Just trying to feel a little bit of a rhythm, build up on it. I've only been hitting golf balls for a month and a half now, so everything should be pretty close."