NFL insider: Colin Kaepernick's workout with Raiders 'went well,' 'door is open'

Having agreed to a massive contract extension with career-long Raider signal-caller Derek Carr earlier in the offseason, Las Vegas isn't in the market for a starting quarterback, but they did notably lose backup Marcus Mariota to the Atlanta Falcons earlier this year. Other quarterbacks currently on the Raiders depth chart include seldom-used youngsters Nick Mullens and Jarrett Stidham -- who both joined the organization this spring -- and rookie Chase Garbers, who signed with the club earlier this month after going undrafted.

The 34-year-old Kaepernick hasn't played in an NFL game since 2016. The former University of Nevada star was selected by the Niners in the second round of the 2011 NFL Draft, took over as San Francisco's starting quarterback midway through the 2012 campaign and led the team to Super Bowl XLVII, where they fell to the Baltimore Ravens.

Kaepernick started and played in all 16 games for the 49ers in 2013 and 2014, but injuries and struggles on the field led to reduced playing time in his final two NFL seasons. Going into the 2017 offseason, the Milwaukee, Wisconsin native opted out of his contract with San Francisco and became a free agent.

As he went unsigned through the summer, there were allegations that he was being blackballed due to his on-field political statements, most noticeably kneeling during the national anthem of multiple games to protest police brutality and racial inequality. In October 2017, Kaepernick filed a grievance against the league, accusing league owners of colluding to keep him out of the NFL.