Geathers suffered an elbow injury during Monday night's win over the Pittsburgh Steelers. A former starter, Geathers was the team's No. 3 defensive end this year and had no tackles in two games.
The 30-year-old veteran has spent his entire 10-year NFL career with the Bengals (1-1).
Miles was waived Monday and then brought back to fill the roster vacancy left by Geathers. Miles is in his fourth year in the league, all with the Bengals, and has played in 39 games. He led Cincinnati in special teams tackles in 2011 and was second last year.
The Bengals also signed free agent cornerback Curtis Marsh and waived linebacker J.K. Schaffer, who had been promoted from the practice squad for Monday night's game.