Franklin said Allen suffered the unspecified injury last week and did not travel to Friday's game at Illinois. The injury will conclude Allen's career at Penn State. The fifth-year senior has 99 rushing yards and two touchdowns on 24 carries in three games in 2018. He and true freshman Ricky Slade have shared the backup running back role behind junior Miles Sanders.
Allen appeared in 27 games during his first three seasons, starting one in 2015 and recording 65 carries.
"Mark's got a very bright future," Franklin said. "He's going to be very successful at whatever he chooses to do. He's talking about getting a little bit into coaching. We've got a lot of love and respect for Mark about what he's been able to do in his career here."
Slade has 147 rushing yards and four touchdowns, including a 61-yard score Friday at Illinois, on 25 carries this season.