Ex-Liverpool and West Ham defender Song, 40, reportedly fell ill at his home in the Cameroonian capital Yaounde and was immediately hospitalised.
“I wish you a lot of courage and to get well soon, big bro,” former Cameroon striker Samuel Eto’o wrote on social media.
Former Liverpool teammates Jamie Carragher and Robbie Fowler also expressed their support on Twitter.
Song made his name in Europe at French side Metz, joining Liverpool in 1999 after a short spell in Italy. He moved to West Ham in 2000 before eventually returning to France in 2002 with Lens. He switched to Turkish giants Galatasaray in 2004, playing for the Istanbul outfit for four years.
He ended his career in 2010 after a two-year spell at Trabzonspor, and had been working for the Cameroonian Football Federation in recent years.