Sinner hasn't returned to action since winning Wimbledon back in July, missing a second consecutive Masters 1000 tournament following the ongoing Canadian Open.
"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 and wish Bob and his whole team a great and successful event. I can’t wait to be back next year and I’m now focusing on getting ready for the US Open.”
Sinner started the year by winning five straight Masters titles, becoming just the second player alongside Novak Djokovic to clinch every single ATP 1000 crown. The Italian triumphed in Cincinnati back in 2024.
He will be eyeing a full return to fitness for the final Grand Slam of the year at the US Open, where he was defeated by Carlos Alcaraz in the 2025 final. The pair have won 10 of the last 11 majors.
The Cincinnati Open begins on August 13th and will now be without both Sinner and Alcaraz. However, 24-time Grand Slam champion Djokovic is set to participate for the first time since 2023.