World number six Bianca Andreescu is out of the Madrid Open after testing positive for Covid-19, the Canadian confirmed on social media on Sunday.
The 20-year-old said she tested negative twice before flying to Madrid for the tournament, which is set to begin Friday, but was told upon arrival that she had produced a positive test.
"I am feeling good, I'm resting and continuing to follow the health protocols and safety guidelines," she said. "I look forward to getting back out on the court very soon."
Indian Wells order of play - Murray faces Zverev, Swiatek, Tsitsipas in action
The announcement marked yet another disappointment for Andreescu, who won her maiden Grand Slam title at the US Open in 2019 only to suffer a torn meniscus in her left knee a month later.
She was unable to return to competition until February this year, losing in the second round of the Australian Open, and earlier this month made a tearful exit from the Miami Open final against world number one Ash Barty, after tumbling on the court and injuring her foot.
'My serve was absolute crap today' - Andreescu on AO exit
Like numerous other sport governing bodies across the globe, the WTA has said it will encourage players to receive the Covid-19 vaccine but would not require it for competition.
WTA Indian Wells
Pliskova beaten by lucky loser Haddad Maia, Andreescu also out
Indian Wells order of play - Evans, Norrie, Medvedev, Andreescu in Monday's action