Rushel Shell won't be returning to Pittsburgh, a source told ESPN.com on Monday.

Shell asked for his release in April and decided to transfer to UCLA. But the star running back never enrolled at UCLA and instead recently asked the Pittsburgh coaching staff about returning to the Panthers.

Rushel Shell, who had the second-most rushing yards on Pitt as a true freshman, will not be allowed to return to the Panthers after transferring in April, a source said. Charles LeClaire/USA TODAY Sports

However, the door was never open for Shell to return, the source said.

Shell, who arrived at Pitt in 2012 as one of the top running back prospects in the entire country, would have been the featured back for the Panthers in 2013. But Shell asked for time away from football during spring practice to "work through some challenges."

On April 2, the school formally announced that Shell decided to transfer.

Shell is from nearby Aliquippa, Pa., and has twin daughters living in Pennsylvania. The Los Angeles Times reported that Shell changed his mind about UCLA because he felt the distance was too great.

Shell entered spring drills as Pitt's starter after rushing for 641 yards, second-most on the team, and four touchdowns as a true freshman in 2012. He arrived at Pitt after setting the Pennsylvania state record for career rushing yards at Hopewell High in Aliquippa.

Information from ESPN's Brett McMurphy was used in this report.