The Chicago Bears are evaluating all aspects of their defense as they prepare to undergo any Dennis Allen-led changes. One of the biggest differences in personnel will come in the middle of the field.

Linebacker Jack Sanborn’s rise from undrafted free agent to key player on the Bears ’ defense for three seasons was one of the team’s best success stories under former coach Matt Eberflus. Sanborn will rejoin Eberflus after agreeing to a one-year deal with the Cowboys, a source said.