Baltimore announced Callahan's deal Monday. He has appeared in one regular season game during his NFL tenure. The Ravens are the sixth franchise he has played for since entering the league in 2016.
Griffin sustained a broken hand during the Ravens' practice Saturday in Baltimore. He is expected to miss several weeks of practice, including training camp and possibly the preseason.
Callahan, 26, completed 5-for-7 passing attempts for 11 yards during his 2017 appearance for the Green Bay Packers. He has also played for the Tampa Bay Buccaneers, Philadelphia Eagles, Cleveland Browns and New Orleans Saints. He completed 28-of-47 passing attempts for 262 yards, one touchdown and one interception in three preseason games in 2018 while with the Eagles.
Callahan will practice with the team Wednesday. The Ravens have their last preseason game Aug. 29 before kicking off the regular season on Sept. 8.
Lamar Jackson will take first team reps, with rookie Trace McSorley and Callahan relegated to backup duties. McSorley and Callahan will likely get the majority of the Ravens' quarterback reps in the preseason.