Gasperini made the confession to La Gazzetta dello Sport newspaper, admitting he felt unwell the day before and during the second leg of their Champions League Round of 16 tie on March 10.
He did not have a fever, so at the time was not considered eligible for a coronavirus test.
It was only in a blood test 10 days ago that Gasperini discovered he had the antibodies and therefore recovered from the virus.
“Valencia CF wish to publicly express our surprise at comments made by Atalanta coach Gian Piero Gasperini which appeared in the Italian press this Sunday, stating that, both the day before and the day of the match played on March 10th at Mestalla, the coach of our opposing team in the UEFA Champions League Last 16 game was aware of suffering symptoms theoretically compatible with those of coronavirus, without taking preventive measures,” read a statement.