Johnson will start Sunday against the Orioles.
The left-handed Johnson, who is out of minor-league options, was expected to compete for a role in the bullpen but could end up in the rotation to start the season. Manager Alex Cora told Peter Abraham of The Boston Globe that Eduardo Rodriguez (knee) and Steven Wright (knee) are unlikely to open the season on the 25-man roster. That leaves a hole in the starting rotation. Cora cited Johnson along with right-hander Hector Velazquez and left-hander Roenis Elias as potential spot starters to begin the season, according to Boston Herald's Chad Jennings.