Director of Christians in Sport, Graham Daniels, has been speaking after the three-time heavyweight world champion died in the US at the age of 74.
A civil rights campaigner and poet who converted to Islam, Ali was admitted to hospital in Arizona on Thursday after suffering from breathing problems.
"My reaction was 'age catches up with all of us. Life is very, very fragile and even the greatest human being in sport or on the planet is not immortal," Graham said.
He added: "It has reminded me of mortality and the importance of being right with the Creator of the universe, through Jesus Christ. I cannot escape thinking like that when I hear of the death of someone like Muhammad Ali."
Ali battled Parkinson's disease for 32 years, with doctors believing the condition was probably caused by the thousands of punches he received.
A funeral for the sporting icon, who was born with the name Cassius Clay, will be held in his home town of Louisville in Kentucky.
Prior to Thursday's admission, Ali was last taken to hospital in early 2015 to receive treatment for a severe urinary tract infection.
Making his final appearing in public, Ali seemed increasingly frail attending the annual charity-fundraiser event 'Celebrity Fight Night' in Phoenix, when he wore sunglasses and was hunched.
Reflecting on Ali's legacy, Graham Daniels went on to say: "I grew up with Ali as 'king of the world' from the 1960s right through to the early 1980s when he stopped boxing so he was very formative in my experience of sport as a young man.
"From the height of his career, he'll be remembered as a really funny guy and a brilliant boxer but, at the same time, he was a significant civil rights campaigner."
In a statement, a spokesman said the Ali family "would like to thank everyone for their thoughts, prayers and support" and requested privacy.
Muhammed Ali's friend and fellow boxer, George Foreman, said: "Muhammad Ali was one of the greatest human beings I have ever met. No doubt he was one of the best people to have lived in this day and age."
Former heavyweight champion Mike Tyson posted a message on Twitter which read: "God came for his champion. So long great one. @MuhammadAli #TheGreatest #RIP."
Ali is survived by Lonnie, his fourth wife, and a number of children.
You can listen to Graham Daniels from Christians in Sport speaking with Premier's Alex Williams by clicking here: