Staff and media are also prohibited from taking the accessories into the ground, while it is unclear whether the ban extends to Pep Guardiola and his players.
The decision follows trouble when the two sides met in Manchester a fortnight ago.
A Napoli fan was jailed for five months for his part in an attack in a pub near the Etihad Stadium where belts were used as weapons.
Kevin Parker, general secretary of the Manchester City Supporters Club, has branded the rule in place for the Group F fixture "ridiculous".
"It's absolutely crazy," he told the Daily Mail. "I know they have had issues with Napoli fans using belts as weapons but since when has that been a thing in England? Why, all of a sudden, should City fans be banned?"