Andy Murray (36) pulled out of the Cincinnati Open late on Monday as the Briton continues to recover from an abdominal strain in a bid to compete in the US Open that begins later this month.
Murray withdrew from last week's Canadian Open before his round of 16 clash with eventual champion Jannik Sinner due to the issue he picked up after spending nearly five hours on court in wins over Lorenzo Sonego and Max Purcell.
The three-times Grand Slam champion and former world number one travelled to Cincinnati where he hoped to be fit in time to face Russian Karen Khachanov but he will now be replaced by a lucky loser, men's tennis governing body ATP said.
Murray is currently number 36 in the world - his highest ranking since hip resurfacing surgery in 2019 - and was named in Britain's Davis Cup team for their Finals group stage ties that will take place after the US Open.