This is the time in the golf season when the PGA Tour play-offs have usually concentrated minds of leading male golfers.

It has been that way for the past 15 years. With the majors over, the race for the most important trophies has been run; now it is time to cash in.

Formats have changed, the tinkering endless, but the ethos has remained the same; play well all the way to East Lake and try to hit a multi-million dollar jackpot.

This was the lucrative behemoth that confirmed the PGA Tour’s supremacy, a juggernaut to squash less valuable circuits such as the European tour across the pond.

The Florida-based circuit seemed untouchable.

But this week, when the FedEx Cup Play-offs begin in Memphis, there is no such air of certainty or supremacy. The firmament has changed rapidly and markedly, despite this being the start of a three-tournament period worth $75m (£62m).

After events at TPC Southwind, the 125-man field will be reduced to the top 70 in the standings for the following week’s BMW Championship and then to 30 for East Lake in Atlanta and the Tour Championship.

The eventual winner pockets $18m (£15m). Nice work if you can get it.

But not quite nice enough for those who have been swayed by LIV Golf, which has shaken men’s professional golf to its core thanks to the unprecedented largesse of its $25m (£20.8m) purses and extravagant signing-on fees.

Suddenly, the PGA Tour appears the poor relation. It has been left pleading with its members for loyalty, stressing a sense of history and awareness of the golfing pyramid – the kind of stuff the European tour used to say when its leading lights headed Stateside.

How times are changing.

For the future of the game, the battle on the course in Memphis starting on Thursday is nothing compared with what is now being fought in the US District Court for the Northern District of California.

This is the legal body hearing the case of 11 LIV players, including Phil Mickelson and Ian Poulter, who are contesting their suspensions from the PGA Tour for competing in the opening three Saudi Arabia-funded LIV events.

Indeed, Mickelson – a six-time major winner and runner-up to Tiger Woods in the 2009 play-offs – is currently serving a ban until at least 31 March 2024 for attempting to recruit LIV players.

The ‘LIV eleven’, as they are known, are fighting an anti-trust lawsuit against the Tour.

More immediately, three players – Talor Gooch, Hudson Swafford and Matt Jones – are seeking a temporary restraining order to be allowed to compete in the play-offs.

A ruling on that must be made in time for them to play in Memphis if they are successful. All three golfers are banned from the premises unless and until the case is settled in their favour.

Gooch recently claimed he was surprised to be suspended, hinting that his intention was to only play the LIV opener at the Centurion Club in Hertfordshire in June.

“Historically the Tour has not done that,” Gooch said of the bans.

“So based on the history, that was my expectation,” he added in response to questions over why he decided to join LIV full time.

And the upstart Saudi-funded set-up, which will expand to 14 tournaments next year, is bullish about the legal processes it is funding.

“The purpose of this action is to strike down the PGA Tour’s anti-competitive rules and practices that prevent these independent-contractor golfers from playing when and where they choose,” it said in a statement last week.

The PGA Tour released a memo written to players by commissioner Jay Monahan referring to the 11 players as “former colleagues” who have “walked away from the Tour”.

Monahan described them as “Saudi Golf League employees”, adding: “To allow re-entry into our events compromises the Tour and the competition, to the detriment of our organisation, our players, our partners and our fans.

“The lawsuit they have filed somehow expects us to believe the opposite, which is why we intend to make our case clearly and vigorously.”

This has always been a bitter dispute, a civil war the game has never previously encountered. Differences between tour loyalists and rebels are becoming increasingly profound.

American Presidents Cup captain Davis Love III has even raised the prospect of a players’ strike.

“The nuclear option is to say ‘Fine, if they have to play in our events we just won’t play’,” he said last week.

Both sides are doubling down but more big stars could defect with a double dip, pocketing riches from the FedEx Cup before taking a huge Saudi signing-on fee.

Cameron Smith, lying second in the play-off standings and the current Open champion, did nothing to dispel rumours that he could go when asked in the immediate aftermath of his St Andrews triumph.

What will happen after the Australian competes for the Internationals in the Presidents Cup next month? There are others also rumoured ready to move.

Ordinarily the conversation would currently be centred on the merits of the play-off system as Smith tries to hunt down the leader in the standings, world number one and Masters champion Scottie Scheffler.

Not this year.

As Love III commented: “I don’t know what’s going to happen from here on out, but I know it’s going to be a fight.”

And he was not talking about the golf.