Prince Harry returned to the UK in July for the unveiling, but a party with 100 guests, including Elton John, was postponed to later this month.
Meghan and Harry would be free to fly to the UK after the US lifted travel restrictions to allow quarantine-free travel.
However a spokesperson for the Sussexes has now confirmed to the Sunday Telegraph that the couple will not be attending the bash.
Majesty Magazine editor-in-chief Ingrid Seward, at said of the reception: “You would have thought it would definitely be something Harry would really want to be at.
“I can’t imagine anything less important for him because he would want to respect his mother.
“It is an important gathering of his mother’s friends. He could even get a few quotes for his memoir.
“I am sure Meghan would want to be there for Diana and Harry.”