The PGA Tour has announced schedule changes and prize money increases in order to stem the flow of big-name players joining the rival LIV Golf International Series.

Brooks Koepka became the ninth major champion to sign up to the controversial Saudi Arabia-backed league, rocking the PGA Tour on Wednesday.

The American joined Sergio Garcia, Dustin Johnson, Phil Mickelson, Martin Kaymer, Graeme McDowell, Louis Oosthuizen, Charl Schwartzel and Bryson DeChambeau in the breakaway competition.

Defecting players were indefinitely suspended from PGA Tour events, but were allowed to play at last week's U.S. Open and participate in next month's 150th Open at St Andrews.

The PGA had been rumoured to be mulling over a switch to a calendar-year schedule, alongside increased purses and the creation of new no-cut international events featuring the Tour's top 50 players.

Commissioner Jay Monahan confirmed those alterations at a press conference ahead of the Travelers Championship, stressing the PGA's need to innovate to remain golf's leading competition.

"I want to talk about where the PGA Tour is headed. We don't expect to overcome this current challenge by relying on our legacy and track record alone," he said.

"We've been on a path for a number of years to strengthen and evolve our product for the benefit of our fans and players alike, those plans are obviously accelerated in light of the current environment.

"We have some exciting developments coming out of yesterday's policy board meeting that will further secure our status as the pre-eminent golf tour in the world.

"This includes moving forward with our future product model for the 2022-23 season and beyond, a return to a calendar-year schedule beginning in 2024, with the FedEx Cup contested from January to August, culminating with the FedEx Cup play-offs and followed by the fall events.

"[The Tour will also add] revised field sizes for the FedEx Cup play-offs in 2023 and beyond, [and] the creation of a series of up to three international events, to be played after the conclusion of the fall schedule, which will include the top 50 players from the FedEx Cup points list.

"Alongside these changes, the policy board also amended the resource allocation plan, to increase purse sizes at eight events during the 2022-23 season, with an average purse at $20million. 

"There is more work to be done, and details to confirm, but implementing substantial changes to our schedule gives us the best opportunity to not only drive earnings to our players, but also improve our product and create a platform for continued growth in the future."

Rory McIlroy, a vocal opponent of LIV Golf, had earlier stated he supported the changes, saying to Sky Sports: "I think having the FedExCup season go to a calendar year, that would be a pretty good idea.

"So then it gives guys the opportunity to play if they want to play in the fall, or if they don't want to play in the fall they don't have to, they're not forced to.

"You're trying to give playing opportunities and create prize funds for the lower half of the membership, but also trying to accommodate what the upper half of the membership want as well with an off-season, time away from the FedExCup schedule. So it's a balance."

Monahan added the PGA could not wish to compete financially with the rival tour, headed by two-time major champion Greg Norman, which he described as "irrational".

"I am not naive," Monahan said. "If this is an arms race and if the only weapons are dollar bills, the PGA Tour can't compete with a foreign monarchy that is spending billions of dollars in an attempt to buy the game of golf.

"We welcome good healthy competition, the LIV series is not that. It's an irrational threat, one not concerned with the return on investment or true growth of the game. 

"Currently no one organisation owns or dominates the game of golf, instead the various entities work together to meet our own respective priorities but with the best interests of the game at heart.

"When someone attempts to buy the sport and dismantle the institutions that are intrinsically invested in growth and focus only on a personal priority, that partnership evaporates. 

"Instead we end up with one person, one entity, using endless amounts of money to direct employees towards their personal goals, which may or may not change tomorrow or the next day.

"I doubt that's the vision any of us have for the game."