Ruud, runner-up to Carlos Alcaraz in the 2022 final, will be replaced in the draw by lucky loser Arthur Gea, who takes on Juan Manuel Cerundolo in the opening round.
The 27-year-old Ruud had retired during the second set of his Cincinnati Open meeting with Christopher O'Connell earlier this month and said he had not recovered in time.
"Unfortunately, my back hasn't healed as quickly as we had hoped," Ruud said on Instagram.
"We've been optimistic that I would recover in time, but my team and I have decided that we need to think long term and give my body the time it needs. I'm very sad to announce that I have to withdraw from this year's US Open singles event.
"It's never easy to miss a Grand Slam, but I know this is the right decision. I'll take the time I need to recover properly and come back stronger."
Ruud competed in the revamped mixed doubles tournament last week, partnering Diana Shnaider and the pair were beaten in the quarter-finals by Andrey Rublev and Mirra Andreeva.
US Open 2026
The US Open is the fourth and final Grand Slam of the tennis season, running from August 30th to September 13th. It is a hard-court tournament held at Flushing Meadows in New York City. Follow the links below for more information!
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