Edwards felt discomfort after pitching a scoreless inning Tuesday night in an 8-6 win against the Pirates. An MRI Wednesday revealed the inflammation.
Edwards, 26, is 2-1 with a 2.88 ERA (8 ER/25.0 IP) in 25 appearances.
Right-handed reliever Cory Mazzoni was promoted from Triple-A Iowa. Mazzoni, 28, was 3-2 with a 1.25 ERA in 14 appearances with Iowa this season, striking out 22 and walking five. Mazzoni has not allowed an earned run in his last eight appearances covering 14 innings.
Mazzoni threw a scoreless inning for the Cubs on May 7 against the Marlins.