EXCLUSIVE: Gun coach's advice to Demon against Sinner's 'lethal power'

MELBOURNE: Alex de Minaur's biggest weapons are his heart and his legs and he will need both to be firing at full throttle if he is to give Jannik Sinner the run around at Rod Laver Arena.

The Demon will enter Wednesday's Australian Open quarter-final with a hellish 0-9 record against the world No.1 and defending champion.

The 25-year-old has taken his game to new heights with a more aggressive mindset and a willingness to embrace the crowd and release his emotions.

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The parochial support will help but only count for so much against the ice cool Italian, who continues to shrug off a never ending doping soap opera while racking up wins.

A shaking Sinner looked out on his feet during his fourth round win over Holger Rune before a medical timeout and a snapped bolt at the base of the net revived him.

The 23-year-old was vague about the specifics of his illness and the million dollar question is whether he will be at the peak of his powers against one of the fittest - and fastest - men in world tennis.

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"The shaking... it was obviously deeply concerning for him, it was deeply concerning for all of us watching," Mark Petchey told Stan Sport's Grand Slam Daily.

"We're not entirely sure what's going on with Jannik at the moment in terms of the health scare, but obviously that is something that he's got to manage and it's something that Alex is going to test out in the opening parts of the match - just to see what his physical situation is.

"Jannik does have the luxury of lethal power off both wings, so he can hit winners even when he's feeling completely exhausted."

Petchey, the former coach of grand slam champions Andy Murray and Emma Raducanu, has questioned whether de Minaur is fully comfortable with the burden of carrying a nation's hopes and breaking a painful Melbourne men's drought that dates back to 1976.

Murray snapped a 77-year Wimbledon drought for British men when he beat Novak Djokovic in the final in 2013.

"As great as it is, sitting here saying this is his (de Minaur's) first quarter (in Melbourne), he wants bigger and better things, and he wants to go on and potentially win this tournament," Petchey said.

"He's quick naturally, but he works so hard on it. You don't come up with those kind of finishing shots if you're not doing that back in the lab on the practice court.

"We see him do this day in, day out but he is one of the most exciting players out there on the tour. There's no doubt about that in my mind. It is fun when Alex is out there."

After losing to de Minaur in the fourth round, Alex Michelsen said his serve was obviously weaker than other parts of his game.

De Minaur has worked hard on trying to increase his firepower but there is a trade off with that.

"The one little question mark (against Michelsen) obviously was the first serve percentage (42 per cent)," Petchey said.

"I know he's gone for a bigger first serve and he doesn't make that many - in terms of the top 100 ratio - but he is winning a high percentage of those points. But against Sinner, you feel as though he's going to need both. A quick first serve and a lot of them (on target)."