Terms of the deal weren't disclosed. The club also waived linebacker Ronnie Thornton.
"You know, a good football player at Appalachian State; don’t know a lot about him right now," Bears coach Lovie Smith said of LeGree. "But we have a need at the position. He was out there on the practice field today. We start evaluating him today."
A second-year player, LeGree spent time on the practice squads of three teams -- Arizona Cardinals, New York Jets, and San Francisco 49ers -- as a rookie in 2011 before joining Chicago, which finds itself somewhat thin at the safety position after injuries Saturday to Chris Conte and rookie Brandon Hardin.
Conte suffered what the club believes is a minor shoulder injury, while Hardin could miss an extended period as he waits to undergo an MRI in two weeks on his injured neck, which he hurt early in third quarter of the club's preseason victory over the Washington Redskins.
A three-time all-American at Appalachian State, LeGree hasn't yet made an appearance in a regular-season contest and was cut by the 49ers on Aug. 11.
At Appalachian State, LeGree received credit for playing a role in 11 Mountaineer touchdown drives as a result of the 24 turnovers he forced, which included 22 interceptions and two forced fumbles over his college career.
LeGree's 22 INTs in college rank No. 3 in Appalachian State history, and over his last three seasons, he led the nation in that statistic.