Andy Murray admitted it will be tough to win another grand slam, saying he was back at "square one" in his career after his US Open exit.

The British three-time major winner was well beaten in the second round on Thursday, falling to Canadian 15th seed Felix Auger-Aliassime 6-2 6-3 6-4.

The tournament in New York marked Murray's first grand-slam singles appearance since the 2019 Australian Open, having faced a career-threatening hip injury.

Murray, 33, said he needed more time after struggling to back up following his stunning comeback win over Yoshihito Nishioka, with the first-round clash going longer than four and a half hours.

"I don't know what I was expecting. The number one priority for me was that my hip was good, and it coped really well with a five-set match, which lots of people, myself included, weren't sure how I was going to do with that and actually coped relatively well the other day against a very tough opponent. So that was positive," he told a news conference.

"I feel like I'm back at square one, having not played in slams for a few years, I need to build up my body and my physical conditioning so that I have the ability to back up five-set matches.

"That takes a bit of time, unfortunately. Well, for me, anyway. Maybe other players it doesn't."

Murray last won a grand slam at Wimbledon in 2016, and he has not been beyond the second round at a major in just three appearances since 2018.

We're just glad to have you back, @andy_murray.

Onwards and upwards #USOpen pic.twitter.com/SBvreEhcIp

— US Open Tennis (@usopen) September 4, 2020

While he accepts winning another major will be difficult, Murray will not stop trying.

"I would say even after tonight, I would say I'm more positive about what I could do in grand slams than I was before I came over here. You guys obviously don't know how I was feeling even just a couple of months ago," he said.

"So like I said, to come over here and play, I played a couple of tough matches in Cincinnati and I played certainly one very tough match here, and my right hip felt good. That's really, really positive.

"There are other things that need to get better, but I would say that I'm more positive now than what I was a couple of months ago, that's for sure.

"In terms of winning grand slams again, that's going to be extremely difficult to do. It was hard enough when I had two normal hips. So it will be difficult, but I'll keep trying, like, why not? Why shouldn't I try my hardest to do that?

"And if I don't, that's all right. But I might as well shoot for the stars. And if I don't – yeah, if I don't get there, then that's all right. But I'm trying my best to get the most out of what my body gives me now."