Ramirez, 27, went 0-0 with a 3.65 ERA in 11 appearances for the Reds in 2009. He has appeared in 16 Major League games over the past two seasons -- including four starts -- compiling a 1-1 record with a 2.97 ERA.
Tampa Bay claimed him off waivers from Cincinnati on Nov. 9.
Thursday's move puts the Rays' 40-man roster at 39.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.