US Open 2015: Eugenie Bouchard out of singles after head injury
|Venue: Flushing Meadows, New York Dates: 31 August-13 September|
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Eugenie Bouchard has withdrawn from the US Open women's singles after suffering a concussion.
The Canadian, 21, had already pulled out of the women's and mixed doubles, but had hoped to be able to play in the fourth round of the singles.
It means Italy's unseeded Roberta Vinci advances to the quarter-finals.
Bouchard, seeded 25, "slipped and fell in the locker room and sustained a head injury" after playing in two games on Friday, a tournament statement read.
Earlier, she had triumphed in a lengthy singles match against Slovakia's Dominika Cibulkova and then a mixed doubles match alongside Australia's Nick Kyrgios.
She reached the Wimbledon final in 2014, rising to a high of fifth in the world, before suffering a dramatic slump in form this year.
Her victory over Cibulkova was her third singles win in a row - the first time she has managed that since January.
She had been due to play a women's doubles match with Russia's Elena Vesnina on Saturday.