World number 16 Madison Keys on Thursday said she has tested positive for Covid-19 and is likely to sit out the Australian Open.
The 25-year-old American's announcement came just hours after former world number one and three-time major winner Andy Murray said he too had tested positive for the virus.
"I wanted to let you know that I have tested positive for Covid-19 before I was supposed to fly to Australia," Keys wrote on Twitter.
"I am very disappointed not to be able to play in the coming weeks after training hard in the off-season and knowing Tennis Australia and the tours did so much to make these events happen.
"I am self-isolating at home. I look forward to being back on tour next month."
Keys made the semi-finals of the Australian Open in 2015.