According to AP, the federation said Ronaldo was doing well and had no symptoms.
However, it did not say when he tested positive.
Ronaldo played in the 0-0 draw at France in the UEFA Nations League on Sunday, besides featuring in the 0-0 draw against Spain in a friendly.
The Juventus forward has been dropped from the country's Nations League match against Sweden to be held on Wednesday.
The federation said Ronaldo's result prompted another round of tests for the rest of the Portugal squad.
Everyone else in the team tested negative.
The squad was scheduled to train normally on Tuesday ahead of the match against Sweden in Lisbon.
The PFF confirmed in a statement: "Following the positive case, the remaining players underwent new tests this Tuesday morning, all with a negative result, and are available to Fernando Santos for training this afternoon, in Cidade do Futebol."
The game against Sweden is scheduled for Wednesday.
It pertains to the qualification phase of the Nations League.
Portugal are in League A, Group 3, and they have played three matches in the ongoing UEFA Nations League. They have registered two wins and one draw and lead the proceedings above second-placed France on goal difference.
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