Eugenie Bouchard was forced to withdraw from the US Open ahead of her fourth round match against Roberta Vinci due to concussion.
The Canadian, seeded 25th, suffered a head injury when she slipped and fell over in the locker room on Friday evening.
Last year's Wimbledon finalist pulled out of the doubles and mixed doubles on Saturday but delayed a decision about the singles.
However, a short tournament statement was released on Sunday which read: "Eugenie Bouchard is withdrawing from the women's singles competition at the 2015 US Open due to a concussion."
Unseeded Italian Vinci therefore advances to the quarter-finals.
Bouchard has endured a poor run of form this year after an excellent 2014 but she was showing signs of returning to her best in New York, having reached the last-16 for the second year in a row.