Clippard, 23, is scheduled to make the start in Saturday's game against the Mariners at Safeco Field. He took the loss in his only start for the Nationals last Monday, allowing three earned runs in 4 1/3 innings against the Giants. He was then was optioned to Columbus after the game. Clippard is 4-4 with a 3.41 ERA in 12 starts for the Clippers.
Perez, 30, is 2-5 with a 4.09 ERA in 13 starts this season. He made his last start on June 3 against the Cardinals.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.