She underwent surgery for uterine fibroids and a subsequent health issue that was initially misdiagnosed as Sjogren’s syndrome. It resulted in a 16-month layoff, and she just returned last month at the Citi Open in Washington, beating Peyton Stearns and losing her next three, including Monday to Muchova.

Venus Williams, at age 45, returned to the US Open and took No. 11 seed Karolina Muchova to three sets before losing in the first round.