The U.S. attorney's office says Richard Khamir Hurd, 26, pleaded guilty Thursday in federal court in Waco.
Prosecutors say Hurd contacted one of Griffin's agents in June with a demand of $1 million in order not to release information damaging to the reputation of Griffin, who won the Heisman Trophy at Baylor.
The agent contacted authorities, who arranged for Hurd to be offered $120,000 in exchange for his signing of a non-disclosure agreement.
Hurd signed the agreement and collected the money, then was arrested. He faces two to three years in prison at sentencing Nov. 21.
Leaving court Thursday, Hurd responded to a request for comment with, "Sic 'em, Bears," the Waco Tribune-Herald reported.
Copyright 2012 Associated Press