Johnson and DeChambeau have joined the likes of McIlroy, Tiger Woods, Jon Rahm, Collin Morikawa, Justin Thomas and Brooks Koepka in resisting the overtures of a Saudi-backed rival circuit spearheaded by Australian Greg Norman.

And McIlroy believes that is the final nail in the coffin for the rebel league as he also took aim at the "naive, selfish, egotistical, ignorant" comments from Phil Mickelson, who had accused the PGA Tour of acting like a "dictatorship".

Asked after his final round of the PGA Tour event at Riviera Country Club if the threat of a breakaway league was over, McIlroy said: "Yeah, yeah. Who's left? Who's left to go?

"I mean, there's no one.

"It's dead in the water in my opinion.

"I just can't see any reason why anyone would go."

Sunday's announcements from Johnson and DeChambeau came three days after Mickelson's motives for potentially joining a breakaway league were laid bare in an extraordinary extract from a new biography of the six-time major winner.

"Who's left? Who's left to go? I mean, there's no one. It's dead in the water in my opinion." - Rory McIlroy.

In an interview with Alan Shipnuck for his forthcoming book, Phil: The Rip-Roaring (and Unauthorized!) Biography of Golf's Most Colorful Superstar, Mickelson claimed the new league is an attempt at "sportswashing" by the Saudi regime.

The 51-year-old also admitted he has concerns about Saudi Arabia's human rights record in a telephone interview with Shipnuck last November, adding: "They're scary mother******* to get involved with.

"Knowing all of this, why would I even consider it? Because this is a once-in-a-lifetime opportunity to reshape how the PGA Tour operates. The Tour likes to pretend it's a democracy, but it's really a dictatorship."

Asked about Mickelson's comments, McIlroy added: "I don't want to kick someone while he's down obviously, but I thought they were naive, selfish, egotistical, ignorant.

"It was just very surprising and disappointing, sad. I'm sure he's sitting at home sort of rethinking his position and where he goes from here."