CHARLOTTE, N.C. — Carolina Panthers defensive coordinator Mike Trgovac has turned down a contract offer and won't return in the biggest shakeup yet to coach John Fox's staff.

Team spokesman said Charlie Dayton said today that Trgovac informed Fox and general manager Marty Hurney of his decision at the Senior Bowl practices in Mobile, Ala.

Trgovac becoming the fourth assistant to leave since the end of the season. The move comes less than a week after star defensive end Julius Peppers told the Panthers he didn't want to return after he becomes a free agent next month.

Trgovac joined Fox's staff in 2002 as defensive line coach and was promoted to defensive coordinator a year later when Jack Del Rio left to coach the Jacksonville Jaguars.