Clay, the 2009 Big Ten Offensive Player of the Year, finishes his career seventh on Wisconsin's all-time rushing list with 3,413 career yards and fifth in rushing touchdowns with 41.
"This is the right decision for me at this time and I'm excited to start a new chapter," Clay said in a statement.
Clay, a fourth-year junior who turned 23 earlier this week, met with Wisconsin coach Bret Bielema Friday afternoon to discuss his options. He started two seasons for the Badgers and earned third-team All-America honors this fall despite being slowed by a knee injury in November.
"Since coming to Wisconsin, John has gone above and beyond all of our expectations both on and off the field," Bielema said in a statement. "His tremendous production on the field speaks for itself, but we are also proud of him as a teammate and the work he has done in the classroom and off the field. We support his decision and wish him luck."
Adam Rittenberg covers Big Ten football for ESPN.com. He can be reached at firstname.lastname@example.org.