Andy Murray has been added to the US Open main draw after Swiss former champion Stan Wawrinka withdrew.
Murray, who won his first Grand Slam title at the tournament in 2012, withdrew from the men's singles at the Tokyo Olympics with a thigh strain.
Meanwhile, fellow Briton Dan Evans lost in the Canadian Open first round.
And three-time US Open winner Novak Djokovic, 34, pulled out of the Cincinatti Masters warm-up tournament to focus on the US Open.
The Serb is bidding to win all four Grand Slam events in the same year.
"I am taking a bit longer to recover and recuperate after quite a taxing journey from Australia to Tokyo," Djokovic said.