Roach, 27, signed with the Raiders despite Bears General Manager Phil Emery's efforts to keep him in Chicago, the report said.
The Chicago Tribune reported Emery said Wednesday he would like to keep Roach with the team, but officials are pressed against the salary cap.
The Tribune said it is not yet known whether Roach's departure will affect the team's negotiations with middle linebacker Brian Urlacher, whose hamstring injury left him sidelined during the final four games of last season, making Roach a starter.
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