Janzen Jackson of the University Tennessee football team poses for a photograph during media day at Neyland Stadium in Knoxville.

KNOXVILLE - Janzen Jackson's return barely lasted six weeks.

University of Tennessee football coach Derek Dooley dismissed the Volunteers' star safety on Wednesday, according to a release from the school.

"Our program has devoted a tremendous amount of energy, resources, support, and care in an effort to help Janzen manage his personal challenges," Dooley said in the release. "I will always be there to help him as a person, but there comes a time when a player's actions preclude him from the privilege of playing for the University of Tennessee football team.

"Although I'm disappointed with this outcome, we will never compromise the long-term organizational values and goals we maintain here at Tennessee."

ESPN.com, citing sources, reported that the reason for Jackson's dismissal were multiple failed drug tests. Sources told the Times Free Press that substance-abuse was at the center of the reason for Jackson's absence but would not confirm that a failed drug test was the final straw.

Jackson withdrew from UT in February for the same personal reasons that kept him out much of the Vols' preparations for the Music City Bowl last December. That absence lasted five months, and the junior reenrolled in school in July. Dooley had praised Jackson's play during preseason camp, and the Vols were experimenting with Jackson at the nickelback spot to take advantage of his aggressiveness and playmaking ability.

The Vols will have neither of those now.

"He's day-to-day in the program and he has been," Dooley said after practice on Tuesday morning. "To his credit he's been working hard on the field and we hope he continues to maintain the right level off the field. I've told you guys from the beginning, I've always operated as if he wasn't here and we're going to continue to do that. But he is here and he's doing good, it's day-to-day and today is good.

"If he's managing what he needs to manage the right way, day-to-day, then yeah, I guess you can use it. There's no margin of error, I think it's fair to say there's no margin of error -- and there won't be."

Those comments appear to indicate whatever caused Jackson's dismissal might have occurred sometime after Tuesday's practice and before Wednesday's dismissal. The Vols have a mock game tonight at Neyland Stadium to wrap up fall camp, and afterward Dooley will address the media.

Jackson was a preseason second-team All-Southeastern Conference selection, and with Herman Lathers sidelined until October with a fractured ankle, he essentially was the Vols' leading returning tackler.

His dismissal will end an ongoing saga of off-field issues for Jackson, who missed three games as a freshman for two separate suspensions. He missed one game for violating team rules and two more following his involvement in a failed armed robbery attempt with two teammates.

More coverage online and in Thursday's Times Free Press. Follow Vols beat writer Patrick Brown on Twitter for more continuous updates.