Two-time major winner Dustin Johnson says he's excited by what the upstart Saudi-backed LIV Golf series has to offer and it could be good for golf despite a divisive start.

World number 12 Johnson, speaking on the eve of the PGA Championship, said in February he was committed to playing on the US PGA Tour, which has refused releases for members to play in LIV Golf's opener next month in London.

But with the richest purse in golf history at $25 million on offer and more huge paydays planned for eight events worldwide this year, LIV Golf has some players pondering a jump from established tours.

"I think golf is in a good spot and I think what they're doing could potentially be good for the game of golf," Johnson said. "I'm excited to see what happens here in a few weeks."

But the 37-year-old American made clear the limits of what "excited" meant for him.

"I'll be watching," Johnson said.

Johnson won the 2016 US Open and 2020 Masters and a victory this week by the 2019 and 2020 PGA runner-up would put him on the brink of a career Grand Slam.

Ninth-ranked American Jordan Spieth, who can complete a career Slam with a victory this week, backed the US PGA Tour as he noted the choice some players must make.

"The Saudi league, or the LIV league, everybody can do what they want to do," Spieth said. "No players are standing in any players' way. If they want to go, go. I love where I'm at. I've been saying that for a long time."

Phil Mickelson, who won last year's PGA to become at age 50 the oldest major winner in golf history, is not defending his title after comments revealed in February that LIV Golf's Saudi backers were "scary" with a "horrible record on human rights."

Mickelson, who said he wanted to use LIV Golf as leverage against the US PGA, hasn't played since, the left-hander saying he needed time away from golf.