Ramirez, a left-handed reliever, is 1-1 with a 2.59 ERA in 15 relief appearances this season while working exclusively out of the bullpen for the first time in his career.
Starter Jose Contreras went down with a ruptured left Achilles' tendon in the second inning on Saturday, forcing the White Sox to spring to action and make the move.
It is likely the White Sox will use Ramirez in the rotation, but with the planned demotion of reliever Boone Logan coming Sunday, they may decide to use him out of the bullpen and call up one of their Minor League starters.
In six Major League seasons with Atlanta (2003-06), Seattle ('07) and the Royals ('08), Ramirez has gone 39-30 with a 4.53 ERA in 121 games, 104 of which were for starts. His best season came as a rookie with the Braves in '03, when he was 12-4 with a 4.00 ERA in 29 starts.
Ramirez will wear No. 49 with the White Sox.
Orlando is hitting .262 with nine home runs, 42 RBIs and 73 runs scored with Class A Winston-Salem. He also added 15 doubles, 12 triples and 28 stolen bases with the Warthogs.
David Just is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.