Pelfrey, who had Tommy John surgery on the same elbow in 2012, had scar tissue removed Tuesday to relieve pressure on a nerve. The problem had been causing tingling in his fingers since spring training and led to reduced velocity on his pitches.
The surgery was performed by Dr. James Andrews, who also operated on Pelfrey in 2012.
A nine-year veteran who has also pitched for the New York Mets, Pelfrey is 0-3 with a 7.99 ERA in five starts this season.
Pelfrey has been sidelined since May 2 with a strained left groin, and his velocity dropped even more while he was pitching at Triple-A on a rehab assignment. That led to tests, which revealed the nerve issue.