Novak Djokovic is once again the talk of the Australian Open after footage emerged of the fourth seed receiving a message taped to his water bottle from his entourage during his quarter-final win over Russian Andrey Rublev on Wednesday.

The Serbian superstar, 35, who is chasing a 10th career Grand Slam title at Melbourne Park, was the recipient of some instructions from his team sitting in the stands at Rod Laver Arena.

The incident unfolded in just the third game of the first set.

It follows a paper note attached to another bottle being passed on to ATP tour supervisor Gerry Armstrong, who hand-delivered it to Djokovic during his second round match versus Enzo Couacaud.

Many tennis fans have long formed the view different rules seem to apply for Djokovic.

Was it supplements advice on the bottle ? A stirring message to stay focused? We will never know.

While there could be a valid explanation, the predictable silence from the Djokovic camp - and the man himself - will only fuel further rumours.

At the Australian Open, verbal on-court coaching is permitted - but only if players and coaches are on the same side of the court, News Corp reported.

Signals and handy gestures are also allowed if players are on the other side of the court.

The conspiracy theories are set to continue after Djokovic's physiotherapist Ulises Badio was nabbed preparing a 'mysterious potion' in the stands at a tournament last November.

When members of the Serbian's support team then attempted to block the camera's view, eyebrows were raised.  

Djokovic's wife Jelena later clarified everything on social media nothing 'dodgy' had occurred.

Not everyone courtside in Melbourne is hoping Djokovic wins through to Sunday's final.

One supporter encouraged Rublev to 'send him home', which enraged the fed up Serbian.

The 35-year-old returned to Melbourne Park for this year's tournament, having missed the 2022 event after the Australian government infamously deported him due to his vaccination status.

Djokovic was clearly upset by heckling from the Rod Laver Arena crowd during his straight sets quarter-final triumph.

He was heard urging umpire James Keothavong to take action after the fan was reportedly heard yelling: 'Send him home Rublev, send him home'.

When Rublev was serving at 4-1 down, Djokovic said to the umpire: 'Can you tell the front guy to shut up or not? Every point, every single point you're not reacting.'

Then, after winning the first set, Djokovic continued: 'I don't mind if he is supporting him [Rublev]. But for three or four times in a row, he has said things about me.' 

Djokovic has had his fair share of run-ins with fans during this year's tournament, having complained of a fan who was 'drunk out of his mind' in the early rounds.

Speaking about the rowdy crowd, Djokovic said: 'What I have a problem with is when somebody's crossing the line, numerous times...and saying things that were not respectful at all.'

Djokovic, who said the heckling had been going on for more than an hour and a half, added: 'I had enough, you know?'

He next faces US rising star Tommy Paul on Friday for a spot in the final.