Rafael Nadal can't confirm Australian Open participation after hip problem in Brisbane

Rafael Nadal says he will have to wait and see if he is able to play in the Australian Open after needing medical treatment during a tough loss to Jordan Thompson at his comeback tournament.

Nadal looked poised to claim another straight-sets win at the Brisbane International when he brought up a first match point in the 10th game of the second set but missed a backhand overhead.

Two more chances followed in the tie-break but Nadal was unable to take either and Australian Thompson fought back to claim a 5-7 7-6 (6) 6-3 victory after three hours and 25 minutes.

More concerning was the off-court medical time-out Nadal took at 1-4 in the deciding set, although he was able to continue without too much apparent discomfort.

The 37-year-old had surgery on the psoas tendon in his left hip in June after being sidelined since suffering an injury at last January's Australian Open and revealed the latest problem is in the same area.

"I feel the muscle tired," he told reporters in Brisbane.

"I mean, for sure it's not the same like last year at all because when it happened I felt something drastic immediately. Today I didn't feel anything. The only problem is because the place is the same, you are a little bit more scared than usual.

"I need to see how I wake up tomorrow morning. We have been talking these last days, talking about the positive things. That's why I am not over-positive when I have been talking.

"I have been talking with a lot of precaution because I know after a year is difficult for the body to be playing tournaments at the highest level. When the things are becoming more difficult, you don't know how your body is going to react.

"I hope it is not important and I hope to have the chance to be practising next week and to play Melbourne. Honestly, I am not 100 per cent sure of anything now."

Nadal added later on Instagram: "I had a small sensation, not a good one, in a similar place where I had the surgery, but it's too early to say anything.

"Hopefully it's a charged muscle and in the next days I'll make some more tests. If it's only a charged muscle it's been a very positive week."

Thompson will take on second seed Grigor Dimitrov in the semi-finals, while top seed Holger Rune faces Russian Roman Safiullin.

In the women's event, top seed Aryna Sabalenka continued to look sharp in a 6-1 6-4 victory over Daria Kasatkina, her 14th straight win in Australia, while second seed Elena Rybakina was a set up on Anastasia Potapova when the Russian retired.

Sabalenka will take on fellow Belarusian Victoria Azarenka in the last four after she battled past Jelena Ostapenko, while Czech Linda Noskova won the battle of the teenagers against 16-year-old Mirra Andreeva.

At the ASB Classic in Auckland, defending champion Coco Gauff and second seed Elina Svitolina both eased into the semi-finals, while Alexander Zverev defeated Stefanos Tsitsipas to help Germany defeat Greece in the United Cup quarter-finals.

Meanwhile, Harriet Dart reached the biggest final of her career at the WTA 125 event in Canberra, battling to a 7-5 3-6 7-5 victory over American Katie Volynets, and Heather Watson is through to the doubles final in Brisbane with Belgian Greet Minnen.

READ MORE: Novak Djokovic on wrist injury ahead of Australian Open: I think I'll be OK