World number one Jannik Sinner has withdrawn from this week's Cincinnati Open because of a knee injury, but still expects to be fit for the US Open later this month. "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. The Cincinnati Open main draw begins on 13 August, with the final on 23 August. Zverev and 24-time Grand Slam champion Novak Djokovic are among those in action. The US Open, the last Grand Slam of the year, takes place in New York from 30 August to 13 September.