Tsitsipas in pain but hopes to be fit for Australian Open

World number four Stefanos Tsitsipas has admitted he has been struggling with pain at the ATP Cup after elbow surgery but is hoping to be "at 100 percent" for the Australian Open.

The Greek star lost his first singles match since going under the knife in late November, losing to Argentina's world number 11 Diego Schwartzman 6-7 (5/7) 6-3, 6-3 on Monday night.

He showed no outward signs of being in discomfort but later said he had felt the injury and it had affected his serve.

"I'm in a little bit of pain. That's normal. I served more serves than I have ever served in the last month," he said.

"There was fatigue at the end, but, you know, I tried to avoid the pain."

The 23-year-old had right elbow surgery after pulling out of the ATP Finals in Turin.

He said the recovery had been better than expected, even if it was still a work in progress.

"It gets better and better every single day," he said.

"My serve did let me down, but I think we have plenty of time before the Australian Open begins, and I think if I take the right precautions and follow what my doctor says, then I can see myself performing at 100 percent at the Australian Open.

"Going into that surgery, even the doctor was unsure if it was a good idea to perform and play the Australian Open.

"My recovery was much better than he would have expected in comparison with some other players that he has treated in the past, so he was surprised."

The opening Grand Slam of the year starts at Melbourne Park on January 17, with Tsitsipas gunning for his first major title.

He made the semi-finals in Australia last year, losing to Russia's Daniil Medvedev.

It remains to be seen whether he continues his comeback with another singles match at the ATP Cup on Wednesday when he is due to meet Georgia's Nikoloz Basilashvili.

"That was one of the biggest concerns if I'm going to play this match (against Schwartzman), how is the recovery going to be," he said.

"I'm really hoping to be able to walk on the court and practise some serves without pain. That's my biggest goal right now."

Greece has no chance of making the semi-finals of the 16-team event after losing their opening two ties.