Novak Djokovic expects to be back in full shape for the Australian Open starting next week after a wrist injury prevented him from finding his best level during a 6-4, 6-4 defeat by Alex de Minaur on Wednesday.

Djokovic suffered his first defeat in Australia for six years as De Minaur put the hosts on course for a 2-0 win over Serbia in their United Cup quarter-final.

“I knew that probably, (I was) not going to be at 100 per cent physically, emotionally, mentally game-wise in the opening week of a season. Neither did I expect that,” Djokovic, who had to have treatment on the wrist for the second day running, told a press conference.

“I was not on my level but it was just one of these days where I didn’t feel my best on the court, and (my) opponent played very well.”

However, the record 10-times Australian Open winner appeared optimistic about overcoming the wrist issue ahead of the first Grand Slam of the season.

“I think I’ll be okay, to be honest,” he said.

“(The wrist injury) did have quite an impact, particularly on the forehand and serve. (But) I have plenty of time, I think enough time to get myself in the right shape for the Australian Open.

“The process is not strange to me. It’s not unusual. I’ve been in this kind of situation so many times and I know what I need to do along with my team to get myself ready... I hope that I will not be injured this time around.

“That’s what we’re going to work on, to get my body in the right shape, optimal state, so that I can perform at the high level throughout hopefully the entire Australian Open.”

De Minaur sent 15th-seeded Australia to their first appearance in the United Cup semi-finals.

"It's extremely special," said world No. 12 De Minaur, who won 33 out of 34 points behind his first serve to claim his first win over a world No. 1.

"Novak's an unbelievable competitor and what he's done for the sport is pretty special. It feels surreal, it feels amazing and I'm happy to do it here in Perth and in Australia.

"Ultimately when you go against Novak, you've just got to go out there, try and enjoy, back yourself and no matter what, keep fighting till the end. Today was my day. I'm happy I was able to get the win. This one definitely means a lot."