The 31-year-old Kaepernick, who threw 72 touchdown passes and rushed for 13 scores from 2011-2016, has been out of the league for two seasons since his six-year 49ers tenure ended.
During his final year, Kaepernick protested social injustice by taking a knee during the national anthem. He hasn't been able to find a pro job since, and the quarterback filed a grievance against the league that was eventually settled out of court in February.
As for where the Dolphins could turn at quarterback, that remains a mystery.
Jake Rudock and Luke Falk are the two remaining Dolphins on the depth chart.
The 26-year-old Rudock has played three career games, completing three of five passes for 24 yards and an interception. The Detroit Lions selected him in the sixth round of the 2016 draft.
The 24-year-old Falk was a Titans sixth-round pick in 2017 and has not seen live game action.
Rudock and Falk could hypothetically develop into starters down the line, but giving one of them a shot now is a risky proposition.
The Dolphins have to figure out a solution but have few options.
They could look to draft a quarterback in 2019, but it's possible the three top options (Oklahoma's Kyler Murray, Ohio State's Dwayne Haskins, Missouri's Drew Lock) are gone by the time Miami picks at No. 13. Matt Miller of Bleacher Report currently has that trio going in the top 10, with no other signal-caller picked in the first round.
They can alternatively look to trade for Arizona Cardinals quarterback Josh Rosen, provided the loud chatter connecting Murray and the Cards (discussed here via Josh Weinfuss of ESPN.com) rings true. Rosen was the 10th overall pick of the 2017 NFL draft.
The best remaining free agent on the market is arguably ex-Jacksonville Jaguars quarterback Blake Bortles, who has shown flashes of why he was drafted third overall in 2014 but who was also benched twice last year in the midst of a trying season.
Kaepernick could be an intriguing stopgap of sorts if the team is looking to essentially punt the 2019 season in hopes of drafting a superstar signal-caller in 2020 with better draft position. Although the first half of his 49ers tenure (which included two NFC Championship Game trips and one Super Bowl appearance) was far more successful than the second half (three seasons out of the playoffs), the 49ers experienced much turmoil as the team had three head coaches from 2014-2016.
Kaepernick could fare better in a more stable situation under first-year head coach Brian Flores.