European football's governing body is reluctant to switch the second leg of the last-16 tie to an alternative venue but is wary it may be necessary, its vice-president Michele Uva indicated.
A surge in COVID-19 positive tests in and around Barcelona has led to a local voluntary lockdown, with residents asked to stay at home for a fortnight.
Napoli are due to visit Barcelona for an August 8 fixture, and UEFA remains hopeful the game will be able to go ahead behind closed doors.
A plan B would almost certainly see the match switched to be played in Portugal, where UEFA will stage the quarter-finals, semi-finals and final of the competition later in August.
Uva told Italian broadcaster Radio Punto Nuovo: "Barcelona-Napoli? Napoli officially goes to play in Barcelona unless rules prohibit playing in Spain in the meantime.
"We hope that does not happen and the second legs will be played in the cities they belong to. Obviously there are back-up solutions."
Napoli held Barcelona 1-1 in Italy when the first leg was played on February 25, before the coronavirus pandemic closed down football across most of Europe.