Keothavong has returned to Europe after the US hard-court stretch
British number one Anne Keothavong retired from her first-round match at the second-tier ITF event in Torhout, Belgium, because of illness.
Keothavong, ranked 53, was trailing world number 271 Irena Pavlovic from France 6-2 3-1 when she pulled out.
The Briton had stepped down to the ITF level event ahead of the clay season.
"Anne has had a cold virus coming into this week and had breathing problems during the match," Keothavong's coach Nigel Sears told her website.
Keothavong became the first British woman since Jo Durie in 1993 to break into the top 50 of the world rankings when she reached 48 in February.