English golfer Eddie Pepperell claims stars who sign up for the LIV Golf Invitational Series are making it obvious "what money means to you".

Former world top-50 star Pepperell says many players are taking "a big risk" by aligning themselves with the series that is being funded by Saudi Arabia's Public Investment Fund.

Former U.S. Open and Masters champion Dustin Johnson, 37, is among the 42 confirmed entrants for the first event, which will be held at Centurion Club near London from June 9-11.

Sergio Garcia, Kevin Na, Louis Oosthuizen, Ian Poulter, Charl Schwartzel, Graeme McDowell and Lee Westwood are also set to feature in a tournament that will have 12 teams and 48 players.

There have been claims of the event being an attempt at sportswashing, and while Pepperell did not level that accusation, he suggested a lust for money had to be the prime motivation for players who have gone against the wishes of the PGA Tour and European Tour by agreeing to take part.

"From a ROI [return on investment] perspective, the field for the first LIV event is awful," Pepperell wrote on Twitter. "Obviously they're banking on that changing over time. You have to wonder how long they'll keep pouring that amount of money into this if that change doesn't come quickly.

"Plus, deteriorating financial conditions across the world may have an impact. Nobody will be impervious to what we're seeing and what we'll continue to see economically into the next 18 months.

"The players who have signed up should be upfront and honest about their reasons to do so. And it has to be the money. There's nothing wrong with chasing money or higher salaries, people do it across all industries.

"It's somewhat understandable from the older guys… But to those under 35/40 who have signed up, you have taken a big risk. And it shows to the rest of us (peers included) how little commitment you have to your respective Tours (who have done a lot for you), and ultimately what money means to you."

The inaugural tournament clashes with the Canadian Open on the PGA Tour, an event at which Johnson is a previous winner.

Rory McIlroy described the Canada event and this week's Memorial Tournament as "proper golf tournaments" on Wednesday, as he reflected on the LIV Series line-up.

"I certainly don't think the field is anything to jump up and down about," McIlroy said of the Centurion Club tournament.

Northern Irishman McIlroy has tempered his comments on the LIV Series in recent months, having previously been robust in his opposition.

He understands its appeal to some, but has been quite clear he will not be taking part.

"Some guys are in a position where they are not guaranteed a job next year. It's hard to stay in the top 125, especially when you're in your 40s and maybe don't hit the ball as far as you've used to. As we've seen, it's a young man's game nowadays," McIlroy said.

"So if another entity comes along and says, 'we'll guarantee you this amount for three years', plus you're playing for a ton more prize money, you're playing fewer events and you can spend more time with your family it's very appealing to some of those guys that are in that position."

Phil Mickelson had long been linked with the LIV Series, but the 51-year-old has not played since apologising for comments made about the Saudi Arabia regime and has not been included on next week's start list. The American said in February he was taking a break from golf and did not defend his US PGA Championship last month.