The former Wimbledon finalist had been due to face Stefanos Tsitsipas in the first round on Rod Laver Arena on Monday in one of the plum ties of the first round.
But on Sunday afternoon the tournament announced he had withdrawn with a right foot injury, making it the fourth time in the last eight grand slam tournaments where he has not been able to play a match.
The popular Italian, a semi-finalist in Melbourne in 2022, has been off the tour since suffering an ankle injury during his second-round match against Arthur Rinderknech at the US Open.
He had previously missed the French Open because of an abdominal injury, while in 2022 he also sat out Roland Garros following hand surgery and then tested positive for Covid-19 ahead of Wimbledon.
Once ranked as high as world number six, the 27-year-old, beaten by Djokovic in the Wimbledon final in 2021, is now down at 125.
He has been replaced in the draw by Belgian lucky loser Zizou Bergs, who will take on Tsitsipas on Monday.
Fourth seed Jannik Sinner, one of the favourites for the title following his stellar end to 2023, began his campaign with a straight-sets win over Botic Van De Zandschulp.
Sinner, who beat Djokovic twice in a matter of days at the ATP Finals and Davis Cup in November, was a 6-4 7-5 6-3 winner on Rod Laver Arena.
The Italian did not play a warm-up tournament after his late finish to last season, and he said: “I feel like I started off actually really well for the first match.
“Then after, I had some moments where I made a couple of wrong choices, but this can happen. Even if you made maybe some matches, this can happen. Maybe you are a little bit tired sometimes.
“It was important today for me because I was looking forward to stepping on the court.”
Former finalist Marin Cilic played his first grand slam match since the US Open in 2022 following knee surgery but was beaten in four sets by Hungary’s Fabian Marozsan.