
Jannik Sinner of Italy serves to Carlos Alcaraz of Spain during the men's final of the Cincinnati Open at Lindner Family Tennis Center. AFP
The withdrawal comes a day after illness forced Sinner to concede defeat to great rival Carlos Alcaraz after going 5-0 down in the first set of the Cincinnati final on Monday.
The 24-year-old did not speak to journalists after the loss, issuing a statement saying only that he would definitely play at the US Open in New York, where the singles main draw starts on Sunday.
"I love Grand Slams a lot, they are the main tournaments for, for my season and my career," reigning US Open champion Sinner said.
"The US Open is going to be a tough tournament, but in the same time, I'm looking forward to it if I'm ready, physically and mentally."
The statement did not address his participation in the mixed doubles -- organised on Tuesday and Wednesday in a new shortened format that brings together the world's best singles players -- raising doubts about whether he would be able to compete.
The pair replacing Sinner and Siniakova will face Switzerland's Belinda Bencic and Germany's Alexander Zverev in the first round.
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