Andy Murray and Karen Khachanov pulled out of the Western & Southern Open in Cincinnati ahead of their scheduled first-round match on Tuesday morning.
Both cited injuries, with hopes of recovering in time for the U.S. Open, which begins Aug. 28 in New York.
Murray, 36, withdrew from last week's National Bank Open in Toronto because of an abdominal injury. The Scot was set to face eventual champion Jannik Sinner of Italy in the round of 16.
Murray is a two-time champion in the Masters 1000 event in Cincinnati.
Khachanov, who is recovering from a stress fracture in his back, has not played a singles match since losing to Novak Djokovic in the quarterfinals of the French Open on June 6.
Khachanov, a 27-year-old Russian, was the No. 11 seed in Cincinnati.
The two were replaced by lucky losers Daniel Altmaier of Germany and Alexei Popyrin of Australia. Popyrin won in three sets.
—Field Level Media