Duke's DL stint is retroactive to June 17, the day after he made his most recent start.
"We just want to make sure to stop it now so it doesn't become something that lingers for the rest of the season," said Duke, who had a similar injury cost him two-and-a-half months in 2007. "[I want to] make sure we get it right and take it slow."
Duke would be eligible to return on July 1, but general manager Neal Huntington said he expects Duke to miss two more starts before rejoining the rotation. Duke already had his start skipped on Tuesday. Having to miss just two more outings is, of course, the best-case scenario.
An MRI confirmed that Duke's injury is solely muscle-related, as the exam found no indication of ligament damage. Duke described it as a collective decision not to have him return to the mound on Wednesday to test out his elbow.
"I'm feeling better," he said. "It's showing improvement. It's a little slow, but I just want to make sure it's right before I start it up again."
Huntington said the organization is walking through the options of finding a replacement for Duke's scheduled start on Saturday. Prior to Wednesday's game, Huntington listed Charlie Morton, Dana Eveland, Daniel McCutchen and Brian Burres all as candidates. Eveland can be crossed off that list now, though, after being used in a 58-pitch relief outing on Wednesday.
Not only was Eveland largely ineffective in the appearance, but the workload was too much for the Pirates to be comfortable calling him back out on two days' rest.
Though Duke said he didn't feel any discomfort in his pitching elbow until midway through his June 16 start, the Pirates are hopeful that a few weeks off will be what he needs to get back on track. After winning his first two starts, Duke has just one win. He has a 5.49 ERA in 14 starts, and opponents have batted .332 against him.
"Obviously, that wasn't Zach," manager John Russell said. "When Zach's on, he's a different guy. When we get this out of there and get him back to full strength, I think we're going to see what we're supposed to see."