MELBOURNE: World number 21 Alex de Minaur was forced to pull out of the Australian Open on Thursday with an abdominal injury, robbing the men's singles draw of one of its strongest local challengers.

The Australian number one, who was also forced to pull out of this week's Adelaide International, said he had suffered a "four-centimetre Grade 2" abdominal tear representing his country at the ATP Cup.

The 20-year-old, who reached the third round at Melbourne Park and won three ATP Tour titles last year, conceded that despite intensive treatment, he was just not in a position to compete at his home Grand Slam.

"It's not a joke, it's something real serious ... even getting out of bed hurts, every day activity hurts," he told reporters at Melbourne Park.

"It's not great. Not going to lie. Obviously, it's a week of the calendar that I really look forward to and put in all the hard work for, so it's pretty devastating to miss out on my home slam."

So desperate was he to play, De Minaur pondered serving under-arm but was persuaded not to take to the court for fear of making the injury worse.

"I just did not want to miss playing here," he said.

"Even though it killed me, it's the right decision. Now I've just got to look at what's ahead."

De Minaur said he first felt the injury early on in Australia's ATP Cup campaign -- in which he registered singles victories over Alexander Zverev and Denis Shapovalov -- and did not regret playing through the pain in his country's cause.

While local Ash Barty will be top seed in the women's singles, Nick Kyrgios will now be the top ranked Australian in the men's draw at world number 26.

"It is tough news, hopefully fingers crossed it's nothing too serious and he can recover as soon as possible," Kyrgios told reporters.

"I had a feeling he was going to do some big things this Australian Open the way he was playing ..."

Australian former world number 17 Bernard Tomic slumped out of the first round of qualifying at Melbourne Park this week complaining of breathing difficulties in the bushfire smoke.

The last Australian to win the men's singles title was Mark Edmondson in 1976.