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.
Boston schools pull out free condoms over wrapping complaints
Aaron Carter is still in love with Hilary Duff