Richard Khamir Hurd, 26, pleaded guilty to one count of interstate communication of a threat related to extortion. He faces two to three years in prison when he's sentenced Nov. 21.
The U.S. attorney's office said Hurd, a former walk-on basketball player at the school where Griffin won the Heisman Trophy, contacted one of Griffin's agents in June with a demand of $1 million in order not to release information that would damage the quarterback's reputation.
According to an FBI affidavit, Hurd first gave the agent a deadline of June 18 but extended it to give the agent time to discuss the offer with others.
Griffin's agent contacted authorities. Under the FBI's direction, the agent reached an agreement to pay Hurd $120,000 for the information and his signature on a non-disclosure agreement. Hurd arrived June 22 at a law office to sign the paperwork and collect the check. FBI agents arrested him afterward.
Hurd's attorney didn't immediately return a phone message.
Leaving court Thursday, Hurd responded to a request for comment with, "Sic 'em, Bears," the Waco Tribune-Herald reported.
Griffin was drafted No. 2 by the Redskins this year and signed a four-year deal for more than $21 million. He has thrown for 747 yards and four touchdowns in three games. The Redskins are 1-2.
A team spokesman declined to comment.