Russell, who played three seasons with the Oakland Raiders, has worked his weight down to a reported 265 pounds, shedding 50 pounds over the past couple of months.
That weight loss led to interest from multiple teams who want to evaluate the quarterback.
NFL.com is reporting Russell's workout is "information gathering in case" and that it is unlikely a tryout is imminent.
Russell has not played football in the NFL since 2009, winning just seven of 25 starts during his career with the Raiders. Russell made approximately $39 million in his career and completed 52.1 percent of his passes for 18 touchdowns, 23 interceptions and a passer rating of 65.2.
More from ESPN.com:
Initially, the Bears weren't interested in taking a look at Russell, and one source believed nobody in the NFL would take the quarterback's comeback seriously until he shed a significant amount of weight. With three quarterbacks already on the roster in Jay Cutler, Josh McCown and Matt Blanchard, the Bears are contemplating whether they want to bring in a fourth quarterback to take to training camp. Currently, the team likes what it already has on the roster, and isn't looking to bring in a fourth quarterback.