The broadcaster, citing three unnamed sources, said the college sports body is probing whether the Texas A&M quarterback was paid thousands of dollars to sign sports memorabilia during a visit to the Jan. 7 BCS National Championship Game in Miami.
The broadcaster said the probe centers on allegations Manziel was compensated by sports merchandise broker Drew Tieman for the signings.
The sources said they witnessed the signings, but no money exchanges.
Should the signal-caller be found in violations of commercial compensation rules, he could be ruled ineligible.
Manziel won the Heisman as a freshman last season after leading the Aggies to an 11-2 record and win over Oklahoma in the Cotton Bowl.