Zavada did not show up for the club's physical exams Sunday night and was not in attendance at the club's first pitcher and catcher workout Monday.
Zavada's agent, Barry Meister, said that his client experienced some discomfort in his shoulder, which was the reason for his absence. Zavada underwent Tommy John surgery last May and threw off a mound for the first time recently.
"He just needed a couple of days to figure out what was going on with his shoulder," Meister said.
General manager Kevin Towers said that Zavada's absence would not be held against him.
"I think the rehab process is often difficult for guys," Towers said. "And the last week or so throwing the ball, he probably didn't feel right and wasn't real happy with where he was at and was contemplating whether he should go through the grind of the rehab process. And I think the more he had time to think about it, he decided he's going to give it a shot.
"[He] probably had a 24-to-48 hour period where he had some doubts, but it sounds like he's focused on coming here and continuing the rehab process and hopefully pitching in the big leagues again."
Zavada was a key contributor to the D-backs' bullpen in 2009, when he compiled a 3.35 ERA in 49 games. He struggled with his command during Spring Training 2010 and, after being sent down to the Minors, he struggled in April before being diagnosed with a torn ligament in his elbow.