Should I stay or should I go? Three sports stars who retired too late

Serena Williams insists she remains "motivated" to keep playing tennis despite her fast-approaching 41st birthday and the absence of a Grand Slam title since 2017.

After her latest Wimbledon setback, should the 23-time major winner retire and preserve her legacy?

AFP Sport looks at three stars who called it quits too late:

Muhammad Ali

Arguably the greatest heavyweight boxer of all time and comfortably one of the 20th century's most influential sportsmen, Muhammad Ali won the world title for the first time in 1964 at the age of 22 with a sensational defeat of Sonny Liston.

His fights against Joe Frazier and George Foreman are legendary landmark moments.

In 1978, he was stunned by an unknown Leon Spinks before avenging the defeat later that year to become the first fighter to claim the world heavyweight title on three separate occasions.

Ali retired, quickly changed his mind and agreed to fight Larry Holmes in Las Vegas in 1980.

Holmes was untroubled by an out-of-shape Ali, who was past his best. "Rocky" actor Sylvester Stallone described the ugly spectacle as "watching an autopsy on a man who is still alive."

For the first time in his career, Ali lost on a stoppage.

Despite calls to retire, Ali fought again in 1981 at the age of 39 against a 27-year-old Trevor Berbick before a series of farcical exhibitions damaged his legacy.

Ali was estimated to have taken nearly 200 000 blows in his career and was diagnosed with Parkinson's disease in 1984. He died in 2016 at the age of 74.

George Best

Manchester United footballer George Best's extravagant skills on the pitch were matched only by his colourful adventures off it.

With his long hair and rock star looks, the Northern Ireland winger was even dubbed the "Fifth Beatle" and helped United