The NCAA is reportedly investigating whether Heisman Trophy winner Johnny Manziel received compensation for signing hundreds of autographs this past January during his trip to the Discover BCS National Championship Game.

Three sources told ESPN's "Outside the Lines" that the Texas A&M quarterback collected a five-figure flat fee during his stay in Miami for signing memorabilia which included photos, footballs and several other items at the request of a broker named Drew Tieman.

Two of the sources claim they witnessed the signings, though neither saw an actual money exchange.

If the NCAA's investigation concludes that Manziel violated NCAA Bylaw -- accepting money for promoting or advertising the commercial sale of a product or service -- he could be ruled ineligible.

Manziel took the college football world by storm in 2012, becoming the first freshman to win the Heisman Trophy award and leading the Aggies to an 11-2 record and a victory over Oklahoma in the AT&T Cotton Bowl.