Contacted by French press agency AFP, Blatter's spokesman Klaus Stoehlker confirmed that Blatter was under medical evaluation and that it was for "stress" because of the pressure he has faced in recent weeks.
Blatter's daughter Corinne told the Blick daily that her father had been forced to cancel all of his appointments through November 15.
Blatter has been at the centre of controversy since a corruption storm hit FIFA just ahead of his reelection to a fifth term in May. Blatter said days later he would stand down.
But last month, Blatter and UEFA president Michel Platini were suspended for 90 days by FIFA's ethics committee, as Swiss authorities conduct a criminal investigation into alleged criminal mismanagement at the scandal-tainted world governing body.
Before he was suspended, Blatter, who has been in charge of FIFA since 1998, had said he would step down on February 26, when a FIFA congress elects a new president.