The move was retroactive to Aug. 14.
President of baseball operations Dave Dombrowski told reporters the injury is "brand new" and the club will seek a second opinion from Dr. James Andrews.
According to Dombrowski, Sale told the training staff on Friday about stiffness he felt on Wednesday and Thursday. The lefty had an MRI Saturday, which revealed the inflammation. There is no timetable for his return.
The Red Sox said Sale was not available for comment.
Sale is 6-11 with a 4.40 ERA in 25 starts this season and has struggled with consistency. However, in his past two outings, the 30-year-old had a 1.84 ERA with 25 strikeouts and two walks.
Heading into Saturday's games, the Red Sox were 17.5 game back from the Yankees in the AL East and 6.5 games back from the wild card.
To fill Sale's roster spot, the Red Sox recalled righty Ryan Brasier from Triple-A Pawtucket.