Jannik Sinner, the world's No. 1 men's tennis player, has suffered a major injury setback after withdrawing from the Cincinnati Open on Sunday because of a right knee injury.

Sinner, who has not competed since capturing his second consecutive Wimbledon title last month, had already withdrawn from the National Bank Open in Toronto, which began on Wednesday. The Italian superstar was hoping to use the Cincinnati tournament as part of his preparations for the upcoming US Open.

The 24-year-old has five Grand Slam titles to his name and is still chasing the French Open title that would complete his career Grand Slam.

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Jannik Sinner Confirms Cincinnati Open Withdrawal

Sinner confirmed his withdrawal in a statement released by Cincinnati Open tournament officials, revealing that his right knee remains a concern despite working with his medical team.

"After consulting with my doctors and my team, I have to announce that I need to withdraw from the Masters 1000 tournament in Cincinnati," Sinner said.

"My right knee has been bothering me and even though we have been working hard with my medical team, I have to accept that I'm not ready to compete yet.

"I’m very disappointed not to be able to play in Cincinnati. I can't wait to be back next year and I'm now focusing on getting ready for the U.S. Open."

The withdrawal will be a significant concern for Sinner with the US Open approaching. The hard-court Grand Slam is one of the biggest tournaments on the tennis calendar and represents his next major opportunity to add to his Grand Slam tally.

Sinner And Alcaraz Both Miss Cincinnati Open

Sinner's withdrawal comes just days after his biggest rival, Carlos Alcaraz, also announced that he would miss the Cincinnati Open.

Alcaraz revealed on Tuesday that he was withdrawing from the hard-court event because of a lingering wrist injury. As a result, tennis fans in Cincinnati will not get to see either of the world's top two players when the men's singles competition begins on Saturday.

The absence of Sinner and Alcaraz is a major blow for the tournament, particularly given their recent rivalry at the biggest events in the sport.

Cincinnati Open Holds Special Memories For Sinner

Cincinnati has been a particularly successful venue for Sinner in recent years.

The Italian won the Cincinnati title two years ago before going on to claim his maiden US Open crown. The tournament has traditionally served as one of the final major preparations for players ahead of the US Open.

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Last year, however, Alcaraz defeated Sinner in a four-set US Open final to claim the title.

With both players now missing Cincinnati because of injuries, attention will turn towards their respective recoveries and whether they will be fully fit when the US Open gets underway.

For Sinner, the immediate priority will be recovering from his knee problem and ensuring he is ready to compete for another Grand Slam title.