The team made the move after the hard-throwing reliever blew save chances on successive night in games against the Cincinnati Reds.
Surgery will not be required, but general manager Neal Huntington told the Pittsburgh Tribune-Review before Wednesday's contest at Cincinnati's Great American Ball Park that Capps is expected to be sidelined for as long as eight weeks.
"The good news is this is something we caught early," Huntington said. "It's something we can handle before it would turn into a labrum tear."
Huntington did not say who would fill the closer's role in Capps' absence.
In 37 games this season (40 1/3 innings), Capps is 2-3 with 17 saves and a 3.12 ERA.
The newspaper report added that Capps will spend four weeks on a rehab program, followed by another four weeks on a return-to-pitch program.