US president Barack Obama will not attend Muhammad Ali's funeral, the White House has confirmed.
Obama and his wife Michelle will be in Washington for their daughter Malia's high school graduation ceremony, a spokeswoman for the president said.
Ali's widow Lonnie spoke to Obama over the phone and appreciated his "kind words and condolences," family spokesman Bob Gunnell said.
The Obamas are sending a letter to be read at Friday's service in Louisville, Kentucky, where White House senior adviser Valerie Jarrett - who knew Ali personally - will represent the president.
Up to 15,000 people are expected to attend the funeral at the KFC Yum! Centre, which follows a procession through the streets of the boxer's home town.
Ali died in Phoenix, Arizona, last Friday aged 74. The three-time world heavyweight champion had been admitted to hospital earlier in the week with a respiratory condition having suffered with Parkinson's disease for 32 years.
The cause of death was septic shock due to unspecified natural causes, his family said.
Hana Ali, one of the boxer's nine children, shared the last photograph she took of her father, less than two weeks before he died.
She posted the image on Twitter with the caption: "My last photo of my beautiful father ... telling him I love him on May 22, 2016."
Two of Ali's daughters, Rasheda and Maryum, will speak at the funeral, along with Ali's widow Lonnie, former US president Bill Clinton, American actor Billy Crystal and Malcolm X's daughter Attalah Shabazz.
Turkish president Recep Tayyip Erdogan and King Abdullah II of Jordan will no longer address the congregation, a spokesman for the Ali family said, but they are expected to attend the service, which will be open to the public and live-streamed on the internet.
Former world heavyweight boxing champion Lennox Lewis and Hollywood actor Will Smith - who portrayed Ali in the 2001 film about the boxer's life - will be among the pallbearers.
The others will be Jerry Ellis - the brother of Jimmy Ellis, Ali's former sparring partner and fellow world heavyweight champion - and Ali's cousins John Grady and Jan Wadell, nephew Ibn Ali, former brother-in-law Komawi Ali and family friend John Ramsey.
Ali's funeral will be preceded by a Jenazah - an Islamic funeral prayer programme - which will also be open to the public at midday on Thursday at the Freedom Hall, where Ali made his professional debut with victory over Tunney Hunsaker in 1960.