Three Portsmouth players, James Bolton, Andy Cannon and Sean Raggett, have tested positive for coronavirus.
The League One side said the trio are all self-isolating and the club has notified Public Health England.
All players and first-team staff were tested earlier in the week and the club said they are still awaiting around half of the results of the tests.
“All three players were in good spirits and perfectly calm,” Portsmouth chief executive Mark Catlin said.
“They are showing mild or no symptoms.
“Football is not immune from this virus and I can assure you that it only really hits home when those that you know contract it.”
Portsmouth’s players and staff were tested following their FA Cup tie with Arsenal after several of the Gunners squad had been in contact with Olympiakos owner Evangelos Marinakis on the night of their Europa League meeting.
Marinakis, who also owns Nottingham Forest, confirmed he had the virus on 10 March. Arsenal manager Mikel Arteta subsequently tested positive for coronavirus.