'Devastated' Nick Kyrgios withdraws from the Australian Open

The Australian No 1 announced at a press conference that he had been forced to pull out of the season-opening Grand Slam due to a knee injury.

Kyrgios was due to face Roman Safiullin in the first round on Tuesday, but he will be replaced by lucky loser Denis Kudla in the main draw.

The 27-year-old's injury woes started before the United Cup as he missed the mixed-team event due to injury.

He made a tentative return in an exhibition match against Novak Djokovic at Rod Laver Arena on Friday and was hopeful of being fit for this week's hard-court major.

However, he has been unable to recover in time.

"Obviously extremely disappointed," he said. "I know you guys will all be wondering what's going so my physio Will [Maher] has been with me throughout my career and he's been monitoring me pretty closely the last week and he's going to give you more of the details about what's kinda gone on.

"Obviously I am just exhausted from everything and [it's] obviously pretty brutal in one of he most important tournaments of my career and it hasn't been easy at all."

He added: "It's just bad timing. That's life, you know. injuries are part of sport … I'm not doubting that I'll be back to my full strength.

"Devastated obviously. It's my home tournament and going into this event as one of the favourites, it's brutal."