Gaffney joined the Dolphins in early October. He had the best season of his career last year with Washington, then signed with the New England Patriots and was released at the end of training camp.
Gaffney, however, had just four catches in three games with the Dolphins and missed Miami's game against Buffalo last week because of a knee injury.
Miller has spent most of this season on the Indianapolis Colts' practice squad.
Information from The Associated Press was used in this report.