Prince Afflict returned to the UK in July for the unveiling, but a party with 100 guests, including Elton John, was postponed until the end of the month.
Meghan and Harry will be free to fly to the UK after the US lifts travel restrictions to allow for quarantine-free travel.
However, a Sussex spokesperson has now confirmed to the Sunday Telegraph that the couple will not attend the party.
Ingrid Seward, editor-in-chief of Majesty Magazine, said of the reception: “You would have thought it would definitely be something that Harry would really like to be.
“I can’t think of anything less important to him because he would like to honor his mother.
“It’s an important gathering of his mother’s friends. He could have got some quotes for his memoir as well.
“I’m sure Meghan would want to be there for Diana and Harry.”