Mattison underwent season-ending neck surgery after being rushed to a hospital following an injury he sustained during Sunday's matchup against the Chicago Bears.
The good news is that Mattison is expected to make a full recovery and currently has full strength and motion.
Miami signed running backs Mike Boone and Aaron Shampklin following the move.
Mattison signed a one-year, $1.3 million deal with the Dolphins this past offseason that included $1.1 million in guaranteed money with a $167,500 signing bonus.
The 27-year-old would've entered his seventh year in the NFL this season, spending 2024 with the Las Vegas Raiders and the previous five with the Minnesota Vikings, who drafted Mattison in the third round of the 2019 NFL Draft.
Mattison has made a solid career of being a reliable No. 2 running back option. In 75 games (19 starts) with the Vikings, Mattison posted 3,088 total yards and 17 touchdowns.
Last season, he posted 714 total yards (420 rushing) and 5 touchdowns.