World number one Jannik Sinner, who was forced to retire during the final of the Cincinnati Open, and playing partner Katerina Siniakova have withdrawn from the US Open mixed doubles draw, tournament organizers confirmed Tuesday.

“Jannik Sinner and Katerina Siniakova have withdrawn from the US Open Mixed Doubles Championship,” read a statement on the US Open website.

“The withdrawal comes after Sinner was forced to retired due to illness during the Cincinnati Open final against Carlos Alcaraz on Monday.”

The 24-year-old was forced to concede defeat to great rival Alcaraz after going 5-0 down in the first set of the Cincinnati final due to an illness which struck on the eve of the match.

“I’m disappointed, I didn’t feel great from yesterday,” Sinner said on court. “During the night, I thought I would recover a bit better, but it was not the case.”

Sinner did not speak to journalists after the loss, issuing a statement saying only that he would definitely play singles at the US Open in New York, where the 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 — organized 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.

Sinner and Siniakova will be replaced by the American duo of Danielle Collins and Christian Harrison, who will face Switzerland’s Belinda Bencic and Germany’s Alexander Zverev in the first round.