The good news is that Red Sox general manager Ben Cherington doesn't believe that Johnson's UCL is damaged, and the club will treat the injury conservatively.
Johnson made his Major League debut for the Red Sox on July 21 in Houston and gave up three hits and four runs over 4 1/3 innings. In that start, Johnson's velocity was lower than he displayed in Spring Training, and perhaps the elbow issue was starting to develop then.
Perhaps Johnson -- ranked as Boston's No. 4 prospect by MLB.com -- will recover in time to get another start or two in the Majors before the season ends.
Johnson has made 18 starts for Pawtucket this season, going 9-6 with a 2.53 ERA.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.