Baltimore manager Buck Showalter said, "It's something he gets once a year." Cashner received an injection Wednesday to treat the injury.
It has been a rough season for the 31-year-old Cashner, who signed a two-year contract as a free agent in February.
After going 11-11 with Texas last season, Cashner is 2-9 with a 4.56 ERA and is 0-4 in eight starts since May 21. He gave up five runs in 6⅓ innings against the Yankees on Tuesday after retiring the first 13 batters.
Baltimore recalled right-hander Yefry Ramirez from Triple-A Norfolk. The rookie could start in Cashner's place on Sunday against Texas.