Shell ran for 641 yards and four touchdowns last season as a freshman at Pitt. He saw his heaviest workload -- 79 yards on 25 carries -- in the BBVA Compass Bowl in place of injured starter Ray Graham on Jan. 5.
ESPN Recruiting ranked Shell as the third-best running back and the No. 26 player overall coming out of high school in 2012. He possesses size, speed and power, and was recruited by many schools including Alabama, Florida, Ohio State, Oregon and Tennessee.
Last month, Pittsburgh announced that Shell was taking some time away from football to "work through some challenges."
Shell requested a release from his scholarship to Arizona State, Arizona, Cal and UCLA, but Pitt denied his request to transfer to Arizona State, where former Pitt coach Todd Graham is the coach, a source told ESPN. Shell also wasn't allowed to transfer to Arizona because former Pitt staffers coach there as well.
The 6-foot-1, 215-pound Shell will sit out the 2013 season.
Information from ESPN college football reporter Joe Schad was used in this report.