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Cox's new agent also represents Seahawks safety Earl Thomas, linebacker Bobby Wagner, Packers quarterback Aaron Rodgers, linebacker Clay Matthews and Saints safety Kenny Vaccaro, to name a few.
49ers head coach Jim Harbaugh and general manager Trent Baalke are also represented by Athletes First.
Cox is in a contract year, having signed a one-year, $695,000 contract prior to the 2014 NFL season.
His team-high four interceptions is tied for third in the league entering Week 13.