IRVING, Texas -- Monte Kiffin will not return to the Dallas Cowboys coaching staff in 2015, according to multiple sources.

Kiffin last season served as the Cowboys' assistant head coach/defense -- a nebulous title under which he served mostly as an on-field consultant. In 2013, he was the defensive coordinator for a unit that ranked among the worst in franchise history.

Monte Kiffin was the Cowboys' assistant head coach/defense last season. AP Photo/Ric Tapia

Kiffin's last official duty with the Cowboys was to help coach at the Pro Bowl. He is the only coach who had an expiring contract not renewed other than Bill Callahan, who joined the Washington Redskins as offensive line coach after the Cowboys' season.

A source said that Kiffin, who turns 75 later this month, would like to continue coaching in some capacity.

If he doesn't coach again, it would be the end of a long and productive run as one of the NFL's best assistant coaches. His career was highlighted by his time with the Tampa Bay Buccaneers, where he coached Hall of Famers Warren Sapp and Derrick Brooks and had a top-10 ranked defense in 11 of his 13 seasons from 1996 to 2008.

The Buccaneers won the Super Bowl in 2002, and Kiffin's defense led the NFL in yards and points allowed per game as well as interceptions.

Kiffin left the NFL in 2009 to join his son Lane's coaching staff at Tennessee and spent three seasons at Southern Cal before returning to the NFL with the Cowboys in 2013.

Of his 28 years in the NFL, Kiffin's teams went to the playoffs 14 times, including the 2014 Cowboys.