The brothers were expected to host an extravagant ceremony on July 1 at Kensington Palace, on what would have been their mother’s 60th birthday.
More than 100 of Diana’s friends, families and supporters were due to attend the ceremony but coronavirus rules have forced the princes to scale back the guest list.
All remaining restrictions were expected to be eased on June 21, dubbed “Freedom Day”, but this date was pushed back to July 19 due to a surge in Covid-19 cases across the UK.
According to the Daily Mail, the duo will now oversee a smaller gathering which will include their Spencer relatives.
The large ceremony which was expected to take place on Thursday will now be scrapped and a new date will be arranged for September.
However, it is unclear if Harry will attend.
The statue, which has been created by artist Ian Rank-Broadley, was commissioned in 2017 by William and Harry to mark the twentieth anniversary of Diana’s death.
"Our mother touched so many lives. We hope the statue will help all those who visit Kensington Palace to reflect on her life and her legacy," William and Harry said in a statement at the time.
The statue will be unveiled in the Sunken Garden of Kensington Palace next Thursday.
It will be only the second time the brothers have come face to face since Harry’s bombshell interview with Oprah Winfrey.
The brothers last saw each other at Prince Philip's funeral back in April.