"I had his girlfriend, who confirmed the news to me," Belhassen told AFP, adding that he spoke with the former player again on Saturday afternoon.
"PSG learned with deep sadness of the death today of our former player Modeste M'Bami. The club offers its sincere condolences to his family and loved ones," wrote PSG on its Twitter account.
OM also deplored the "sudden disappearance" of the former Olympian, as did Le Havre, which expressed its "tremendous sadness".
"Sad news. Modeste M'Bami left us at the age of 40... He wore the colors of Sedan for 3 years (2000-2003). We offer our condolences to his family and loved ones", tweeted the Sedan club for its part.
According to the sports daily L'Equipe, the former player succumbed to a heart attack.
M'Bami, born in Yaoundé, began his professional career in Sedan (2000-2003) before joining much more upscale teams such as PSG (2003-2006) then OM (2006-2009).
He then embarked on a journey that had taken him to Spain, China, Saudi Arabia and Colombia.
He had finished his adventure with the pros in Le Havre (2014-2016), where he had lived since and whose club also paid tribute to its former player on social networks.
Cameroonian midfielder Modeste M'Bami (c) during a match with OM against Sochaux on February 1, 2009 at the Bonal stadium © JOHANNA LEGUERRE / AFP/Archives
M'Bami had two French Cups to his name, won with PSG (2004, 2006).
Olympic gold medalist in 2000 and selected 38 times for the national team, he was also a finalist in the Confederations Cup in 2003 and a CAN finalist in 2008 with the Indomitable Lions.
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