Diop made 63 appearances for his country with the highlight of his international career coming at the 2002 World Cup where he scored the first goal of the tournament as Senegal stunned reigning champion France 1-0.
He went on to score two more goals in the competition as Senegal reached the quarterfinals.
On Sunday, FIFA said it was “saddened” to hear of his passing.
Diop started his club career in Senegal before playing for teams in Switzerland and France.
Much of his career was spent in England though, where he represented both Fulham and Portsmouth in the English Premier League.
Nicknamed “The Wardrobe” — Diop was six-foot-five — he won the FA Cup during his time at Portsmouth and the club paid tribute to the versatile midfielder.
‘Forever in our hearts’
After a brief spell at AEK Athens, Diop returned to London to play for West Ham before finishing his career at Birmingham City seven years ago.
“It is with a wounded heart that we’ve heard of your passing. Know that you will remain forever in our hearts even though you left without saying goodbye. RIP,” he said.
Citing unnamed sources, ESPN reported that Diop had been diagnosed with Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig’s disease or motor neurone disease.
Contributed reporting from Martin Goillandeau.