Barack Obama will not attend Muhammad Ali's funeral, the White House has confirmed.
A spokeswoman for the president said Mr Obama and his wife Michelle will instead be in Washington DC for their daughter Malia's high school graduation ceremony.
White House senior adviser Valerie Jarrett - who knew Ali personally - will represent the president, who will send a letter that will be read at Friday's service in Louisville, Kentucky.
Ali's widow Lonnie spoke to Mr Obama over the phone and said she appreciated his "kind words and condolences".
Up to 15,000 people are expected to attend the funeral at the KFC Yum! Center, which will follow a procession through the streets of the boxer's home town.
The service will be open to the public and will be live-streamed on the internet.
Ali died in Phoenix, Arizona on June 3 aged 74. He had been admitted to hospital earlier in the week with a respiratory condition after battling Parkinson's disease for 32 years.
His family said the cause of death was septic shock due to unspecified natural causes.
Two of Ali's daughters, Rasheda and Maryum, will speak at the funeral, along with Ali's widow Lonnie, former US president Bill Clinton, actor Billy Crystal and Malcolm X's daughter Attalah Shabazz.
A spokesman for the Ali family said Turkish president Recep Tayyip Erdogan and King Abdullah II of Jordan will no longer address the congregation but are expected to attend the service.
The pallbearers will include Will Smith, who portrayed Ali in the 2001 film about the boxer's life, and former world heavyweight boxing champion Lennox Lewis.
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 in 1960.