After experiencing a setback in last Friday's minor league rehab appearance for Pawtucket –– from a forearm injury –– Atchison underwent an MRI, which revealed that he may have suffered a torn ulnar collateral ligament in his right elbow.
The reliever is scheduled to go for a second opinion, but if the injury is indeed diagnosed as a torn UCL, Atchison would likely need Tommy John surgery, an operation that could sideline the 36-year-old for at least 11 months.
"We thought he was progressing pretty well, he went to make that rehab outing and felt it the next day really," Red Sox general manager Ben Cherington said. "We had another MRI done, and it showed an injury to the UCL. He's going to get a second opinion, and we'll go from there. He's got an injured UCL.
"When it comes to pitchers, there's no pitcher in baseball that doesn't have some tearing in their elbow or shoulder; it's just a matter of degree. He's got an injured UCL that, with the second opinion, we'll get a little bit more information on, then sit down with Scott and figure out what's right for him."
Atchison was arguably the team's most consistent reliever this year and once considered an All-Star candidate, posting a 2-1 record and a 1.76 ERA in 37 games. Through 46 innings, Atchison has struck out 34 batters.