Sam Riddle told the Detroit News that the $50,000 he received from the Michigan Democratic Party in 2006 was election-year "hush money" to bolster Granholm's campaign against Republican Dick DeVoss.
The newspaper said Wednesday that party officials called the payment a business contract for media consulting, and added that the FBI has not contacted them.
Riddle also said agents also wanted to know about Granholm's connections to Bernard Kilpatrick, a business consultant and father of then-Mayor Kwame Kilpatrick.
Bernard Kilpatrick has close ties to more than one Detroit-area politician who has run afoul of federal investigators, including City Councilwoman Monica Conyers, who pleaded guilty to bribery charges and resigned.
A spokeswoman for the governor told the News the issue was between Riddle and the party.