The team did not give a reason for his release, but ESPN.com's Adam Schefter reports that Rainey was let go for violating team rules.
Rainey signed with the Colts as a free agent last November, playing in two games and returning six kickoffs for 131 yards and four punts for 29 yards.
The team has veteran running back Ahmad Bradshaw and former first-round pick Trent Richardson to carry the load at the position for the time being after running back Vick Ballard tore his Achilles in practice on Friday.
Rainey, 26, was a fifth-round pick by the Pittsburgh Steelers in the 2012 NFL draft. He has 102 career rushing yards and two touchdowns.
- Scooby Axson