Belinda Bencic and Ons Jabeur have both tested positive for Covid-19 after playing in Abu Dhabi.
They are the third and fourth players to have returned positive tests after travelling to the Mubadala World Tennis Championship.
Britain's US Open champion and the 2021 BBC Sports Personality of the Year winner Emma Raducanu withdrew before the start of the tournament.
Rafael Nadal revealed he had tested positive upon his return to Spain.
On Tuesday, his coach Carlos Moya said he had also returned a positive test.
Switzerland's Olympic champion Bencic lost to Tunisia's Jabeur in the sole women's match at the championship.
In a Twitter post, Bencic said: "Unfortunately and even though I am fully vaccinated, I recently tested positive for Covid-19.
"I am currently isolating and taking all precautionary [measures] to get through this as best as possible as I am experiencing quite severe symptoms (fever, aches, chills)."
Jabeur, who is isolating in Tunisia, said she was also experiencing "strong symptoms".
The Abu Dhabi tournament, which also featured Britain's Andy Murray, often serves as a warm-up event for elite players training in the region before heading to the Australian Open in Melbourne.
