Sinner is suffering from a right knee injury and will not play in Cincinnati.
"After speaking with my team, I must announce that I need to withdraw from the competition. My right knee has been bothering me and although we have been working hard with the medical team, I need to accept that I am not ready to compete yet," Sinner said in a statement.
"I'm very disappointed not to be able to play. Now I'm focusing on getting ready for the US Open."
The Masters tournament in Cincinnati will be held August 13–23. The US Open will be played between August 23 and September 13 in New York.
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