Australian Open casualty Simona Halep revealed she struggled to move during Monday's surprise first-round loss to Shelby Rogers as the world number four lamented her knee injury.

Halep was bundled out of the season's first grand slam at Melbourne Park following a 6-3 6-1 defeat against the world number 52.

It was the second consecutive year Halep fell at the first hurdle in Melbourne.

The 2014 French Open finalist highlighted tendonitis in her left knee, having received medical attention at the end of the opening set on Rod Laver Arena.

"She played well. I think she played very high standard. I had pain at my knee," said Halep, who first felt pain at 3-5 in the first set.

"For me, in the second set, was difficult to move anymore, but she deserved to win. She was aggressive, and she hit very strong balls.

"I'm never thinking to withdraw from a tournament, because it's not in me.

"But I tried. I had some anti-inflammatory before the match, and the previous days. But when you have the tension of the match, official match, the pressure, it becomes harder.

"So I had harder pain, and I couldn't do what I wanted."

She added: "I'm a bit frustrated, but you cannot change much. I'm okay. Just looking ahead. It happens, and I just want to be well with the knee. And then I will think about the game."

Halep said the knee issue had been troubling her since the WTA Finals in Singapore, with the Romanian also struggling in Shenzhen leading into the Australian Open.

While she does not require surgery, Halep was asked if her tendonitis could be a long-term problem for future tournaments and the 25-year-old replied: "Can be, yeah. Can be, but I'm not sure now. I didn't see the doctor yet. I need an MRI.

"Probably need some time off to get it well, recovered, because it's difficult to play with the pain, and the knees are dangerous. So I have to take care."