Cain played for the Bears from 2004-05, seeing time on special teams and as a backup linebacker, and served as the long snapper for the final two games last year. He has also played for Tennessee and Jacksonville.
The move announced Monday comes one day after Chicago waived long snapper Brandon Hartson. He initially beat out former CFL player Chad Rempel, who was waived Aug. 18, in a preseason competition to replace Mannelly, but the Bears ultimately decided to part ways with him, too.
Chicago opens the season at home against Buffalo on Sunday.
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