The Raiders considered Kaepernick's workout a "positive," a source said. Las Vegas could be looking for another passer to serve as the backup for Derek Carr despite trading for former New England Patriots quarterback Jarrett Stidham and signing Nick Mullens.
In NFL team workouts, quarterbacks typically throw the route tree on air, implement team-specific offensive principles on the field and meet with coaches. Team workouts are considered less scripted than the player-organized workout Kaepernick has done in the past to showcase his talents to NFL teams.
Kaepernick, 34, hasn't played in the NFL since 2016, the year he began protesting racial inequality during the national anthem. The only other team known to have brought him in for a visit since then was the Seattle Seahawks in May 2017.
Kaepernick recently threw to undrafted receivers for NFL scouts at halftime of Michigan's spring game, at the invitation of Jim Harbaugh, his former coach with the San Francisco 49ers.
Another potential link to Kaepernick is Raiders offensive coordinator Mick Lombardi, who was a 49ers assistant from 2013 to 2016.