The President of Turkey, Recep Tayyip Erdogan, and King Abdullah of Jordan are among the dignitaries scheduled to speak at Muhammad Ali's funeral on Friday.
Thousands of people are expected to join the funeral in his hometown of Louisville, Kentucky.
Former US President Bill Clinton and actor Billy Crystal are also set to speak. Ali died last Friday at the age of 74 in hospital in Phoenix, Arizona.
A spokesman said his death was from "septic shock due to unspecified natural causes".
The three-time world heavyweight champion had been suffering from a respiratory illness, a condition that was complicated by Parkinson's disease.