McEnroe also ranked de Minaur alongside Nadal, Jimmy Connors, Michael Chang and Lleyton Hewitt as one of the most ferociously competitive players tennis has ever seen.

"There's very few guys that come along that play with that intensity, that effort that Alex de Minaur plays with," the former world No.1 told Channel Nine.

"So they (his rivals) are intimidated by a guy who goes out and gives that all-out 100 per cent every single point like it's the last point."

But for all his gushing praise, McEnroe believes de Minaur's best chance of advancing to the last 16 on Friday night - given his gruelling workload of seven matches in the past 10 days - rests with Nadal's battered body breaking down again.

The Spaniard only completed one hardcourt tournament in 2018 and was forced to quit during last year's quarter-finals in Melbourne with a hip injury.

"The good news is he's 19, so the body bounces back a lot quicker," McEnroe said of Australia's big young hope.

"The fact that he had to go five sets against a qualifier and Rafa, who hasn't played much, won easily and likes to make matches physical.

"The question is how is he (Nadal) going to feel? He hasn't played a tournament since the US Open. Will the body, like last year, betray him?

"That's really, to me, de Minaur's hope this particular event.

"I mean, the guy's coming along for sure (as a future) top-10 player, possibly, to me, a multiple grand slam winner if he can fill out a little bit more.

"But, for this match given what's happened, it's going to be a tall order to bounce back and give what it takes.

"We know he'll give 100 per cent but against Rafa you need like 120 per cent."

Australian Associated Press