Murray, who lost in straight sets to Richard Gasquet in Cincinnati earlier this week in his first singles match for seven months, turned down a wildcard entry into the Flushing Meadow tournament amid concerns his body would not be able to cope with five-set matches.
But the qualifiers, which start on Monday, are played over three sets.
And Murray admits his team didn't consider entering, telling the BBC: "I don't know why we didn't really think of it, but it just never crossed my mind until this morning.
"When I woke up, I though, 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."
The 32-year-old's next move is deciding - along with his team - whether or not to enter next week's ATP singles tournament in Winston-Salem.
Murray is already planning on participating in the men's and mixed doubles at the US Open, but is still on the hunt for a partner. Regular colleague Feliciano Lopez has already agreed to double up with Spain's Davis Cup captain Pablo Carreno Busta, leaving the Scot partnerless for the time being.
"Unfortunately [Feliciano] is taken, and a lot of the players have partners now. It's not easy to find anyone at this late notice, but I'm sure we'll get someone," he added.
Murray and Lopez have a second-round doubles match in Cincinnati against Ryan Harrison and Jack Sock, after beating fourth seeds Jean-Julien Rojer and Horia Tecau on Tuesday.
And despite playing just 24 hours after his first singles match since January, Murray said he was feeling "pretty good" on the whole.
"I was a little bit tired, I felt a bit drained - but more mentally rather than physically. I felt fine, so that was positive thing - maybe it showed that I wasn't running enough," he joked.
"I learnt quite a lot from yesterday - about how tough this process is probably going to be, and how long a process it will be until I'm feeling really good on the court again."