And with the recent callup of Barry Enright to fill out the back end of the rotation, Duke, a starter by trade, will get his first experience in the bullpen.
"It's a new challenge," he said. "It will be a different experience."
The 28-year-old has struggled in a starting role this year with a 2-4 record and a 5.47 ERA in nine starts. His D-backs tenure began in late May after he injured his pitching hand on a line-drive comebacker in Spring Training.
D-backs manager Kirk Gibson said he was unsure of the role Duke will fill, but could see him used in both long relief and special left-handed situations.
"He's gotten left-handers out better than he has right-handers," Gibson said. "But we could use him in long relief, obviously. He would give us some length."
Duke, who hasn't pitched since the All-Star break, said he has been preparing the same as he would if he were starting.
"I just prepare everyday to be ready to pitch," he said. "That way, whenever the phone rings and it's my time, I'm prepared to give everything I've got."