The move Wednesday was made with the Bills (4-7) entering their bye weekend off.
At 6-foot-5 and 320 pounds, Unga was first signed by the Ravens as an undrafted rookie free agent out of Midwestern State, where he earned first-team Lone Star Conference honors last season.
The Bills had an open roster spot after releasing third-year cornerback Justin Rogers on Tuesday.
Buffalo is off until hosting the Atlanta Falcons on Dec. 1 in the Bills' annual ''home'' game at Toronto.
AP NFL website: www.pro32.ap.org
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