The Mexican Football Federation says Veronica Charlyn Corral Ang started showing symptoms such as fever and lesions on July 6 and alerted sports authorities.
Tests conducted at the athletes village medical clinic in Toronto confirmed Wednesday that she had chickenpox.
The Games' organizing committee says a foreign athlete contracted the varicella virus before arriving in Canada and is being treated.
Spokesman Teddy Katz says the athlete is in "self isolation" until the contagious period ends on July 12.
He says the athlete's teammates are also being assessed but the majority have been vaccinated or have already had chickenpox and are not considered susceptible.
Katz said Games officials are working with public health officials to manage and monitor the situation.
Canadian team doctor Dory Boyer said he is confident Toronto health officials will be able to prevent an outbreak.
"We're very lucky being in Toronto in that they have a Toronto 2015 host medical services," he said. "They are extremely well-equipped with public health, working in tandem with them, to prevent any type of outbreak, not just for the Canadian team, but of course anybody in the village or any satellite type villages."
While he couldn't confirm that every member of the team had been vaccinated, Boyer said they are all well-educated.
"We have information that goes out to every member of the delegation, all athletes, all staff, all coaches well before the Games as far as recommendations for them coming into this type of environment as far as immunizations, as far as anything regarding their health, not just to prevent an infectious disease like this, but any type of illness they could contract in this type of environment," he said.
The Mexican Football Federation said Ang is being replaced by Nancy Guadalupe Antonio Lopez.