Carlos Alcaraz has admitted to feeling anxious ahead of his US Open title defence following a four month layoff, though the Spaniard insisted he feels great physically and believes the lingering doubts are purely mental.

"I need to come here to practise with these guys to feel the competition once again, and this is really testing," Alcaraz told reporters at a pre tournament media day on Friday, August 28.

"I'm feeling great and that helped me a lot to know right now that it's all in my head," he added.

The 23 year old, who became the youngest player to complete the career Grand Slam after winning in Australia in January, has not played a singles match since withdrawing from the Barcelona Open with a right wrist injury on April 16, subsequently missing both the French Open and Wimbledon.

He returned to action briefly this week, partnering Serena Williams in the US Open mixed doubles, winning their opening match before falling in the second round to Belinda Bencic and Flavio Cobolli.

Pundits noted flashes of brilliance but also signs of rust, including a serve lacking its usual power.

Alcaraz said his coaching and support team had remained fully confident in his readiness throughout the recovery process.

"I gotta trust my people that tell me that it's gonna be fine. So I just have to go 100 percent. So I'm just trying to stay away from that fear," he said.

His campaign begins against Russian veteran Roman Safiullin, with a potential fourth round meeting against Tommy Paul or Alexander Bublik on the horizon, and either Ben Shelton or Arthur Fils possibly waiting in the quarter finals.

Despite the uncertainty surrounding his form, rivals have been reluctant to write off the defending champion.

Second seed Alexander Zverev, elevated to top billing following world number one Jannik Sinner's withdrawal, backed Alcaraz to find his rhythm quickly.

"I expect him to be maybe a bit rusty the first or second match, but once he gets through that, I think he's going to be a contender for sure here," Zverev said.

Ninth seed Taylor Fritz offered a similar assessment, acknowledging the difficulty of returning at a best of five set Grand Slam but expressing confidence in Alcaraz's ability to adapt.

"Coming back after a layoff at a Grand Slam where men play three out of five sets is not necessarily easy to do. But if you can get past those first couple of rounds, you start to feel pretty good. Then at that point there's no reason why he couldn't find form and play really well. Who knows," Fritz said.

Alcaraz also reflected on his enforced break, saying he had made the most of time away from the tour despite the early frustration of being unable to use his arm.

"At the same time, I enjoyed my time with family, with friends, staying at home," he said.

In July, he attended the World Cup final in New York to watch his native Spain beat Argentina, an experience he described warmly.

"It was a really cool experience and really cool moment," he said, calling the chance to see Spain win their second World Cup "a lifetime experience."

Alcaraz will not face great rival Jannik Sinner in New York after the Italian's own withdrawal through injury, extending a gap between the pair that has already stretched across several months.

"We are not gonna see each other for like six months now, seven months. So it's kind of a weird situation, to be honest," Alcaraz said, wishing his rival a swift and full recovery.