Blackmon had surgery last week on a broken left index finger.
The 6-foot-2, 240-pound Fortt was a fourth-round draft pick by New Orleans in 2014 and opened the season on the injured reserve/designated to return list. He was waived Oct. 6 and claimed off waivers by the Bengals the following day. He was waived a week later and signed to the practice squad.
Fortt was one of 12 semifinalists for the Butkus Award after starting nine games for California in 2013. He began his career at Penn State, where he played two seasons (2010-11) before transferring to California.
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