Riley injured his knee on his first play of the game, a 1st-and-goal run up the middle on Idaho's six-yard-line early in the fourth quarter. The 6-foot-1, 210-pounder was helped off the field directly into North Carolina's locker room.
It's the second time in two years that Riley has endured a serious injury to his right knee. He tore the MCL and the PCL and fractured the tibia in his right leg during Kannapolis (N.C.) Brown High School's 2010 season opener.
"His attitude is really good," Fedora said. "He just said he'll be better for it down the road. Nobody knows why it happened; it just happened. It's unfortunate for a young man that worked all of the way back and now he has to go back and do it all over again."
For the season, Riley has rushed seven times for 18 yards.