The tests were carried out ahead of a return to training after a two-month stoppage because of the coronavirus outbreak in Italy. Fiorentina did not name the players and said optional individual training would continue for the rest of the squad.
"The club has proceeded, as per protocol, to isolate those involved," it said. "Tomorrow morning, the rest of the group are scheduled to undergo medical and fitness examinations prior to the start of the optional activity in the field."
Serie A clubs were given permission by the government to restart training this week as part of an easing of lockdown measures although players can only train individually.
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The league is hoping to resume in May or June but that depends on permission from the government.
Earlier on Thursday, Bergamo-based Atalanta said goalkeeper Marco Sportiello, who tested positive in March, had tested negative and would be allowed to restart training.
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