Sepp Blatter has been admitted to hospital in Switzerland, claiming his body is "letting him down".
The suspended FIFA chief's spokesman said Mr Blatter told him: "My brain and heart are fine, but my body is letting me down."
Mr Blatter, who is 79 years old and facing criminal proceedings over corruption allegations, reportedly wanted to remain at home but doctors decided he needed to be examined.
Mr Blatter is suspected of "criminal mismanagement or misappropriation" over allegations relating to suspicion over a "disloyal payment" of 2m Swiss francs (€1.85m) to UEFA president Michel Platini. He denies the allegations.
Mr Platini said the payment "relates to work which I carried out under a contract" and he "was pleased to have been able to clarify all matters" to the authorities. The Frenchman is not accused of wrongdoing.
The opening of the Swiss investigation piled pressure on Mr Blatter.
