Kaepernick posted a video of himself working out in a gym to Instagram and Twitter. The video starts with a counter saying he has been "denied work for 889 days."
Kaepernick's last NFL game was Jan. 1, 2017. The 49ers lost 35-23 to the Seattle Seahawks that day.
Kaepernick filed a grievance in October 2017 against the NFL under the collective bargaining agreement. He alleged the league's 32 owners colluded against signing him to a contract.
Kaepernick kneeled during the national anthem in 2016 to protest racial injustice and police brutality.
Both his and current Carolina Panthers safety Eric Reid's grievances were settled in February.
Kaepernick was 28-30 in 58 career starts with 72 touchdowns and 30 interceptions. He led the 49ers to a Super Bowl berth in February 2013 and an NFC Championship Game appearance the next year.