PHOENIX -- D-backs manager Kirk Gibson is concerned about his bullpen.
Not the way the relievers have pitched as much as how much they've had to pitch.
With the starters struggling mightily early in the season, the D-backs' bullpen has picked up the slack for the lack of innings, and it has added up particularly for Brad Ziegler, Joe Thatcher and Oliver Perez.
Ziegler appeared in 16 of the team's first 30 games while Perez has seen action in 15 and Thatcher 14.
"They've thrown a ton," Gibson said. "I worry about them. That's why the other day against Philly I pretty much just sat most of those guys down. I worry about their careers and their well being."
So far the workload has not negatively impacted their performance. Ziegler (1.26 ERA), Perez (3.95) and Thatcher (2.53) have all thrown well.
"Those guys have been great, they've been pros, they take the ball," Gibson said. "On my part, though, I get concerned about what their future is and how long we can continue to do this. Because we count on them and if we continue to push them, we're not going to be able to count on them because they're going to break down."
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.