The former World No1’s participation at the Cincinnati Open - where he lost to Richard Gasquet in straight sets - was his first singles performance in seven months.
Murray turned down a wildcard opportunity to play at Flushing Meadows, and with the qualifying matches starting next week and played over three sets, he admitted is he having second thoughts over his decision.
"I don't know why we didn't really think of it, but it just never crossed my mind until this morning," Murray told BBC Sport, having felt his body was not in the right condition to compete in a five-set match.
"When I woke up, I was like - I want to play three-set matches. I could maybe test myself there, and if I got through qualifying that might show that I'm ready to play there. But too late, unfortunately."
While Murray’s left it too late to compete in the singles, he can however still participate in next week's ATP singles event in Winston-Salem.
However, as at Wimbledon this year, Murray is hopeful of competing in both the men’s and mixed doubles at the US Open, though the Brit is yet to find a partner for either event.
"It's not easy to find anyone at this late notice, but I'm sure we'll get someone," he added.