"We Stay Sharp," the former San Francisco 49ers quarterback tweeted, including a video of him throwing to New England Patriots wide receiver Kendrick Bourne,
Tennessee Titans running back Derrick Henry, and New Orleans Saints wide receiver Chris Olave.
Bourne responded, "Man, he looks great." He's good-looking. Powerful arm. Arms like rockets. Take a look. He has six years remaining."
The video features Nike-sponsored athletes. The athletes' participation status was uncertain. Fox News Digital didn't hear back from Nike.
In 2016, Kaepernick retired. He played against the Seattle Seahawks on Jan. 1, 2017. He had 2,241 yards, 16 touchdowns, and four interceptions. Kaepernick led the 49ers to a 1-10 record.
Since then, Kaepernick has campaigned for the abolition of police and jails and compared the NFL Draft to a slave auction.
After settling with NFL owners, his two scout-led tryouts failed to land him a contract. In May, he told NPR that the NFL has not made "substantial change" to address social injustice.