The move came one day after Long was chosen a Pro Bowl starter for the third consecutive year. He endured an injury-filled season, including a back ailment that forced him to miss two games after he started the first 61 games of his career.
Long suffered the arm injury in the first quarter of Saturday's loss at New England.
"It's definitely disappointing -- not the way I wanted to end the season," he said. "I'm going to get healthy and come into next year the healthiest I've been in the NFL."
Three other players missed practice Wednesday due to injuries -- running back Reggie Bush (knee), tackle Marc Colombo (ankle) and cornerback Jimmy Wilson (hamstring). Receiver Brandon Marshall (knee) was limited. The Dolphins didn't specify whether the injuries were on the right or left side.
Tight end Anthony Fasano returned to practice after missing last week's game because of a concussion.
To fill Long's spot on the roster, the Dolphins signed running back Richard Medlin from the practice squad. He signed with New England as a rookie free agent in August and was released at the end of training camp.