US President Barack Obama will not attend a memorial to the late boxer Muhammad Ali on Friday, the White House says.
Ali died last Friday at the age of 74 in hospital in Phoenix, Arizona.
World leaders will be among thousands attending Friday's procession and memorial service in Louisville, Kentucky, where Ali was born.
The White House said Mr Obama and his wife Michelle will be at daughter Malia's high school graduation.
They will send a letter to the Ali family with White House senior adviser Valerie Jarrett, who knew Ali.
Among those attending will be the President of Turkey, Recep Tayyip Erdogan, and King Abdullah of Jordan.
British former heavyweight champion Lennox Lewis and actor Will Smith, who once portrayed Ali on screen, will be among the pallbearers.
Former US President Bill Clinton and actor Billy Crystal are also set to speak.
After Ali's death, Mr Obama said he kept a pair of his gloves in his private study below the photograph of Ali beating Sonny Liston in 1964.
Ali would be remembered, he said, "not just as skilled a poet on the mic as he was a fighter in the ring, but a man who fought for what was right. A man who fought for us."
The boxer will be buried in a private service at the city's Cave Hill Cemetery.
The funeral will be broadcast live on the internet.