Atchison has been dealing with a forearm strain since last weekend's series against the Yankees. Despite a four-day respite, Atchison still felt tightness during Friday's appearance against the Rays.
The injury prompted the Red Sox to place Atchison on the 15-day disabled list and promote right-hander Junichi Tazawa. Considering Atchison primarily tosses cutters and breaking balls, the move was necessary since those pitches typically strain the elbow.
"The other night, I just couldn't really let it go like I wanted to," Atchison told reporters in St. Petersburg. "I went out and tried to throw this morning to see how it's feeling. It feels a lot better than it did the other night, but there's still a little bit in there. We're just going to give it a little time to calm down."
But before Sunday's game, Atchison told reporters in St. Petersburg that his injury was minor. The trip to the disabled list is more of a precaution, since his style of pitching wouldn't be conducive to his long-term health.
In his last outing, Atchison tossed 14 pitches and logged 2/3 of an inning, yielding one unearned run. He also struck out a batter.
Through 37 games and 42 innings this season, Atchison has shined in the bullpen, posting a 1.76 ERA and 2-1 record. He's only allowed 37 hits and 10 runs while striking out 34 batters.
Tazawa, meanwhile, bolstered the bullpen in his last major league stint. Back in April, the Japanese hurler tossed 6 1/3 scoreless innings and converted a save in five appearances for the Red Sox.