Former Cameroon international Rigobert Song is in hospital after suffering a "cerebral attack", a member of his family has told the BBC.
The family member also said the 40-year-old was "unconscious" when he was taken to Yaounde Central Hospital.
Song played 137 times for his country and had spells with English clubs Liverpool and West Ham.
He has been working as a coach for Cameroon's football federation following his departure as Chad coach.
Former Cameroon team-mate Samuel Eto'o tweeted in French: "I wish you courage and a speedy recovery big brother."
Ex-Liverpool players Jamie Carragher, Stan Collymore and Robbie Fowler have also sent messages of support, while Liverpool tweeted: "Our thoughts are with Rigobert Song and his family at this time."