Citing sources familiar with the case, news agencies reported Blatter was being investigated by the Federal Bureau of Investigation and US prosecutors.
Blatter, 79, announced his decision to step down at a hastily arranged news conference in Zurich, six days after police raided a hotel in the city and arrested several FIFA officials, and four days after he was re-elected to a fifth term as FIFA president.
Blatter said an election to choose a new president would be held as soon as possible, though a FIFA official said it would probably not take place until at least December.
"FIFA needs profound restructuring," said Blatter, a Swiss national who has been a dominant presence at FIFA for decades.

READ MORE: FIFA scandal deepens as Blatter aide linked to payments

ALSO READ: Sepp Blatter wins fifth FIFA term despite corruption allegations

Latest News from Sports News Desk