Gradkowski, 28, is a former fourth-round pick of the Ravens back in 2012. The Panthers signed Gradkowski to a three-year, $3.15 million contract last year and he set to make a base salary of $875,000 for the 2017 season.
The Panthers recently placed Gradkowski on injured reserve and later released him with an injury settlement.
In 2016, Gradkowski appeared in 10 games for the Panthers and was rated by Pro Football Focus as the No. 33 center out of 37 qualifying players.