Right-hander Tanner Roark has been called up from extended spring training to join Double-A Harrisburg Senators. Pitcher Erik Davis has been placed on the disabled list.
Davis reportedly tweaked his knee last week and it is not considered a serious injury.
Roark was 1-1 with 2.50 ERA in six starts with 33 strikeouts in 2010 with the Senators.
The Washington Nationals have also announced that right-hander Ryan Tatusko has been promoted to Triple-A Syracuse Chiefs.
Tatusko has gone 1-1 with a 5.73 ERA in seven starts for the Senators. He replaces reliever Cole Kimball, who received the call to the big leagues Saturday.
Roark and Tatusko were acquired from the Texas Rangers in the same trade for shortstop Cristian Guzman in July 2010.