The school tweeted pictures of Kaepernick with coach Jim Harbaugh and players.
Harbaugh coached Kaepernick with the San Francisco 49ers for four seasons from 2011 through 2014 before leaving for Michigan in 2015. Harbaugh benched Alex Smith in favor of Kaepernick in 2012, giving Kaepernick an opportunity to rise to a higher profile in the NFL.
Kaepernick, who led the 49ers to a Super Bowl appearance following the 2012 season, last played in the NFL in 2016, the same year he started kneeling during the national anthem to protest racial injustice.
The Associated Press contributed to this report.