Andy Murray pulled out of the Cincinnati Open late Monday with an abdominal strain.
The 36-year-old continues to recover from the injury as he prepares to compete in the US Open that begins later this month in New York. Cincinnati is among some of the tournaments that players view as tune-ups for the Open.
Murray withdrew from last week's Canadian Open before his round-of-16 clash with eventual champion Jannik Sinner due to the strain. He first felt the injury after spending nearly five hours on court in wins over Lorenzo Sonego and Max Purcell.
"Unfortunately, I'm not going to be able to play this evening," Murray told the crowd last week, before the match against Sinner was to begin. "I'm really sorry. I know I feel like I've let you down. I've rarely been in this situation in my career, and I feel terrible."
The three-time Grand Slam champion and former world No. 1 travelled to Cincinnati where he hoped to be fit in time to face Russian Karen Khachanov, but he will need to be "replaced by a lucky loser," the ATP said.
Murray is ranked No. 36 in the world, his highest ranking since hip resurfacing surgery in 2019. He was also named to Great Britain's Davis Cup team for its finals group stage, which begins after the US Open concludes.
Information from Reuters was used in this report.