The 66-year-old Bosnia-born boss, who took over from Brazilian Zico as head coach following the 2006 World Cup finals in Germany, was rushed to hospital after collapsing in the early hours of Friday morning.

"Coach Osim remains unconscious but because of his physical strength and the effectiveness of the treatments that he has received, he is overcoming the worst of the initial danger," Japan Football Association General Secretary Kozo Tashima told reporters on Sunday.

Osim is under close observation at the intensive care unit at a hospital in Urayasu in Chiba Prefecture.

According to Tashima, Osim's family appear tired but are dealing well with the situation after their initial shock.

His son, Amar Osim, coach of J.League side JEF United Chiba, took charge of their game on Sunday, which they lost 3-2 to Yokohama F. Marinos.

The family have received letters and calls of support from all around over the world, from figures including FIFA president Sepp Blatter, former Japan coach Zico, and Serbia Football Association president Dragan Stojkovic.