Ryan Flaherty was penciled into the lineup in place of Roberts, batting ninth and playing second.
Since Roberts returned from a hamstring injury, he's been the regular second baseman, and he has hit at or near the bottom of the order. He's batting .245/.283/.357 in 107 plate appearances this season, including three games at the beginning of the season before he was hurt.
Johnson was scheduled to pitch Saturday for Double-A Bowie in his recovery from a strained left oblique, but he will instead be added to the bullpen. He's been sidelined since June 6 with the injury.
Derek Wetmore is an associate reporter for MLB.com.. This story was not subject to the approval of Major League Baseball or its clubs.