Hollywood star Will Smith, who portrayed Muhammad Ali in the biopic Ali, will join former heavyweight champion Lennox Lewis and family members as pall bearers at a public funeral for "The Greatest" in Louisville on Friday.
Organisers say Ali helped plan his own funeral as a "last statement" to the world.
The charismatic Ali, a dazzling fighter and outspoken civil rights activist who became one of the 20th century's towering figures, died on Saturday (AEST) at age 74 after health problems complicated by a long battle with Parkinson's disease.
The public Louisville funeral will be preceded on Thursday by a family funeral and an Islamic prayer service, held in the 18,000-seat Freedom Hall that hosted Ali's last fight in Louisville, against Willi Besmanoff in 1961.
The following day, Ali's coffin — which arrived in the city on Sunday aboard a private plane, accompanied by his wife and other relatives — will be paraded through the streets for fans from around the world to say goodbye.
"The message that we'll be sending out is not our message, this was really designed and intended by the Champ himself to be his last statement to the people of planet Earth," Islamic studies scholar Timothy Gianotti told reporters in Louisville.
"The love and the reverence and inclusivity that we are going to experience over the coming days is really a reflection of his message."
Smith, who was nominated for a best actor award at the 2002 Oscars for portraying Ali in the film of the same name, is a family friend.
Lewis, 50, who is the last 'undisputed' world heavyweight champion, told Sky Sports Ali, "was like family, like a father" to him.
Both will join family members as pall bearers at the public memorial in a sports arena in the Kentucky hometown of the three-time world heavyweight champion.
Former US president Bill Clinton, comedian Billy Crystal and Turkish President Recep Tayyip Erdogan are among those due to speak on Friday.