Alcaraz, the reigning Wimbledon and French Open champion, knows he needs an excellent, injury-free US Open to return to the top of the world rankings.

"I just stopped training as a precaution," the Spaniard told reporters at his scheduled media day press conference.

"I didn't feel comfortable enough to keep practising in case it got worse. But after a few hours I'm still feeling good," he added, as he seeks redemption at the tournament where he lost his number-one ranking in 2023.

Despite his reassurances to the press, Alcaraz's injury caused renewed concern and led him to cancel his training session with Argentine Francisco Cerundolo.

Alcaraz won his first Grand Slam title at Flushing Meadows in 2022. Since then, he has added three more, including this year's French Open and Wimbledon, and spent 36 weeks as the world's top-ranked player.

However, after beating Novak Djokovic in the Wimbledon final, he fell to the 24-time Grand Slam champion at Roland Garros in Paris 2024. Both players, along with Italy's Sinner, are strong contenders for the final Grand Slam of the year.

In his only scheduled tune-up for the US Open, Alcaraz was knocked out of the Cincinnati Open, uncharacteristically losing his composure as he was beaten in straight sets by French veteran Gael Monfils.

Alcaraz, who later apologised for smashing his racket in frustration, called it "the worst match I've ever played in my career".

However, he insisted on Saturday that the lack of hard court preparation due to this year's unusual schedule of clay-grass to clay, brought about by the addition of the Olympic Games after Wimbledon, was not a problem. "It doesn't matter to me," he said. "Obviously I would have liked to have played more hard court matches before the US Open.

"But it doesn't bother me at all. If I look back a little bit, you know, going into Roland Garros, I didn't have a lot of matches on clay and it turned out pretty well. "And then at Wimbledon, the same thing.

"So I don't want to think it's going to be the same as the last two Grand Slams, but I'm not worried about not having many hard-court matches."

Despite his youth, Alcaraz has shown himself to be well-equipped for the big occasions. He has never lost a Grand Slam final and said he would learn from his defeat in the Olympic final.

"It was a difficult moment for me," he admitted, "to lose the gold medal in a very close match where I had opportunities."

"But, you know, I had a very good player in front of me who was fighting for the same thing as me and he deserved it," said the Spaniard, who begins his tournament at Flushing Meadows on Tuesday against Australia's Li Tu as he seeks a second US Open title after winning in 2022.