Johnson is currently tossing a football in the outfield at Camden Yards. Later, he'll watch the game from the bullpen, providing a fresh arm for manager Buck Showalter.
Johnson is 1-1 with a 7.82 ERA in six games with the Orioles, including one start. He was 2-3 with a 4.11 ERA in 10 games with Triple-A Norfolk, including eight starts.
In other news, the Astros claimed outfielder Eric Thames off waivers after the Orioles designated him for assignment over the weekend.
Prior to tonight's game, the Orioles will hold a moment of silence in honor of fallen Baltimore County Police Officer Jason Schneider. Schneider was killed in the line of duty on August 28.
Schneider's son Brandon will throw out the ceremonial first pitch and more than 100 members of the Baltimore City and Baltimore County tactical units will be in attendance.
Aberdeen is the only Orioles affiliate that is still in the playoffs.