The tie, originally scheduled to be played on Tuesday, September 13, has been moved back due to "severe limitations on police resources and organisational issues" following The Queen's death and away fans will not be permitted for both legs, UEFA said.
A UEFA statement read: "UEFA today announced that the UEFA Champions League tie between Rangers FC and SSC Napoli, originally to be played on Tuesday 13 September, has been rescheduled for Wednesday 14 September at 21.00CET.
"This is due to the severe limitations on police resources and organisational issues related to the ongoing events surrounding the national mourning for Her Majesty Queen Elizabeth II.
"In addition, it was agreed to also postpone the UEFA Youth League game between both teams from Tuesday 13 September to Wednesday 14 September at 15.00CET.
"Away fans will not be authorised at the games, and as a matter of sporting fairness, Rangers' fans will not be authorised for the return legs in Naples. UEFA urges fans not to travel and to respect this extraordinary situation."
The National Police Chief's Council said in a statement that a national policing operation had been activated and that UK Policing was working closely with other organisations to ensure events are held "safely and with the appropriate security".
The NPCC added: "Following the decisions of the Premier League and English Football League to cancel this weekend's matches, we will work with football clubs to try and ensure that, where possible, football fixtures can take place safely when balanced against the requirement to support national events and deliver day to day policing.
"This is a unique situation and we are working closely with everyone involved."