British number one Johanna Konta has pulled out of her second-round tie at the Connecticut Open with a viral illness, tournament organisers say.
The 27-year-old was due to face Spain's Carla Suarez Navarro on Tuesday at New Haven in the final warm-up event before the US Open, which starts on 27 August.
She has also withdrawn from the doubles competition with American partner Nicole Melichar.
World number 46 Konta beat Germany's Laura Siegemund in the first round.
She is the only British woman with direct entry into the main draw of the US Open, but Naomi Broady is now two matches away after upsetting fellow Briton Katie Boulter 6-4 4-6 6-1 in the first round of qualifying on Tuesday.
Boulter, the British number two and seeded second in the qualifying tournament, fought back to level the match but Broady eased into a 4-0 lead in the deciding set before claiming victory in one hour 52 minutes.
Broady, 28, will play Spain's Georgina Garcia Perez in the second round of qualifying.
British number eight Katy Dunne was beaten 6-2 6-1 by Turkey's Ons Jabeur.
Heather Watson, Harriet Dart, Gabrielle Taylor and Katie Swan are the other British women involved in US Open qualifying this week.