Macbeth's advice to himself to take decisive action rather than procrastinate has been proven to have resonance in the 400 years since Shakespeare put the word's into his anti-hero's mouth.

And it's sage (no pun intended) advice to the FFA now as Australian soccer's governing body looks to deal with the consequences of Perth Glory's salary cap breach investigation.

A-League chief Damien de Bohun and his team have been probing the Perth case for several months, ever since the first discrepancies came to light. Glory chief Tony Sage has insisted his club has done little wrong, but that's not the way the FFA see it.

Glory have been much improved this season and have led the league for most of the campaign, giving many pause for thought as to how they could possibly cram as many highly paid players into their squad as they have.

On Thursday, just after the governing body issued the West Australian club with a second show-cause notice, De Bohun suggested that Glory's  breaches were significant.

"The amount of the alleged breaches would place Perth Glory significantly over the salary cap this year," he said.

If that's the case there is no wriggle room on this one once due process and all avenues of investigation have been exhausted.

The FFA must, like Macbeth, act swiftly and decisively: unlike the central figure of Shakespeare's drama, however, they can afford no mistakes and certainly no introspection.

If Glory is guilty, the FFA must be transparent in the punishment, finger the individuals or groups concerned, and take appropriate measures and do so swiftly - certainly before the finals begin.

That should mean not just a hefty fine, but also a points deduction. It should not just be a slap on the wrist.

If the club has rorted the system then they have compromised the integrity of the whole competition and must pay the price accordingly.

David Gallop, the FFA's CEO, has dealt with famous salary cap breaches and rule infractions before in his days running the NRL and has shown himself to be a decisive judge who is keen to hand out Draconian penalties as a warning to the rest of the competition.

Melbourne Storm had to play a season for no points and was stripped of its premierships for its systemic cheating of the NRL salary cap, while the Canterbury Bulldogs were fined $500,000 and stripped of all competition points when they cheated the cap during Gallop's time at the helm of the NRL.

There will be those in the west who will see this as an eastern seaboard plot. There will be one-eyed fans who see it as some sort of penalty for Glory having had the temerity to lead the league for so long this season.

Tempting as it is to play the victim, if Glory is found guilty on the counts they are facing - and it seems, given how upfront the FFA has been in this matter, that they will be - then those fans need to take their heads out of the sand.

Policing the salary cap (which is $2.55 million) is difficult and clubs are always finding creative ways to get around the limits. Fingers will be pointed in other directions. But so far, no other club has come under investigation.

Sydney FC famously broke the cap in their first season when they won the title in 2005-06. The Sky Blues were fined and lost three points from their total the following season - a penalty that many saw as light.

That was a decade ago. Times have changed, the league is more high profile than it was and scrutiny is, inevitably, greater.

It is hard to imagine Glory getting off so lightly this time if they cannot prove themselves not to have been outside the regulations.

They have one week to do so.